1. What are watertight doors and by what means are they controlled ?
2. What special precaution should be observed when passing through a watertight door operated by a hydroelectric system?
3. What is a line-throwing (Lyle) gun and for what is it used?
4. How would you rig a line-throwing gun for use?
5. On what side of the gun should the line be led?
6. How would you counteract recoil in the use of the Lyle gun ?
7. What is a breeches buoy? Describe how it is used.
8. Make a rough drawing of a breeches buoy in action.
9. What is the fire and emergency signal on shipboard ?
10. What is the signal to abandon ship?
11. What are the signals for: lower boats, stop lowering boats, dismissal from boat stations?
12. After reporting aboard a vessel, when should you familiarize yourself with the location and duties of your emergency station?
13. At sea when should you wear your life preserver?
14. What would you do if you saw a man fall overboard?
15. What methods do ships have to combat fire?
16. What are the four main types of fire extinguishers ? How are they used?
17. How is a fire hose faked?
18. What is the meaning of a red flag waved on shore during the daytime ?
19. What is the meaning of a white flag waved on shore during the daytime ?
20. What is the meaning of two flags, a white and red, waved at the same time on shore by day ?
21. How does the fresh-air hose mask operate ?
22. What are the parts of the all-purpose gas mask?
23. What compartments should the all-purpose gas mask be used in ?
24. What association does the all-purpose gas mask have with the flame safety lamp?
25. What are the parts of the oxygen breathing apparatus ?
26. For what is the flame safety lamp used ?
27. Before using the lamp for a test, what precautions should be taken?
28. How is a day at sea divided?
29. Describe the system of watches on shipboard.
30. Describe the system of striking bells on shipboard.
31. Why do you relieve a watch a few minutes before eight bells ?
32. In steering, what is the meaning of the order "Right rudder?"
33. What is the maximum angle of turning efficiency in steering?
34. What is the meaning of the order "Steady as she goes?"
35. What elements affect steering?
36. What is the difference between the
38
question "What is your course?" and "How do you head?"
37. What is the significance of the lubber's line in steering?
38. What procedure do you follow when you relieve the wheel?
39. In relieving the wheel, how many times is the course given and repeated, and by whom?
40. Why is it of great importance to be a conscientious helmsman, especially in wartime?
41. In the tropics, what special precautions should a seaman take to protect himself from the rays of the sun?
42. If light must be used in a blackout, what color should it be and why?
43. What is the difference between the magnetic compass and the gyro-compass?
44. How many methods of reading a compass do you know ?
45. What is a compass and why is it of such importance to the mariner ?
46. Box the compass by both points and degrees.
47. What is a sounding machine?
48. Make a rough sketch of the sounding machine ready for use.
49. What are the methods of determining depth with this instrument?
50. How do you know that you have struck bottom with the sounding machine; what special precaution should be observed in connection with this?
51. What is the hand lead and how is it used?
52. What is meant by arming the lead?
53. What are the markings on a hand-lead line?
54. When you are on lookout, what sighted objects should you report?
55. How is this report made?
56. When you are on lookout duty, how do you scan the horizon and sky?
57. At what times should lookouts be particularly vigilant?
58. How should a lookout be dressed?
59. What is a marlinespike seamanship?
60. What is the bight of a line?
61. What is the standing part of a line?
62. What are the four most important hitches used on shipboard? Can you make these hitches in the dark?
63. What are the advantages of the square knot and the bowline?
64. What is a splice, a fid, a marlinespike?
65. How is rope coiled?
66. What is meant by the terms belay, bend, bitter-end?
67. What is the meaning of heave, kink, jam?
68. What is a lanyard, a lashing?
69. What is meant by marrying a line, paying out a line?
70. What is a strap, a thimble, a toggle?
71. What are the parts of a block?
72. What is a lull tackle?
73. What is a gin tackle?
74. What is a three-fold purchase tackle?
75. How do tackles get their names?
76. What is the difference between a standing part and the hauling part of a tackle?
77. What is a handy billy?
78. What are masts? What are their functions?
79. What are king posts or samson posts? What double purpose do they frequently serve?
80. What is a hound's-band?
81. What is a spanner stay?
82. What is a hatch?
83. What are hatch coamings?
84. What are hatch cleats and wedges?
85. Make a rough drawing of a section of a hatch coaming showing stiffeners, coaming, stay, hatch cleat, hatch wedge, tarpaulins, and hatch batten.
86. What is a strongback?
87. What are king beams?
88. What are hatch covers?
89. How are tarpaulins put on a hatch?
90. What is a heel-block?
91. What is a boom fair-lead?
92. What is head block (cargo block) ?
93. How are masts supported?
94. What is running rigging?
95. What is a topping lift?
96. What are boom guys?
97. What is a bail in terms of cargo gear?
98. What is the difference between a side whip and a hatch whip?
99. What is a jumbo boom?
100. What is a pedestal?
101. What is a preventer?
102. What is a stopper?
103. What is the purpose of an anchor?
104. Name and describe three types of anchors.
105. What are the three main types of chain link?
106. Name three types of chocks.
107. Name four types of mooring lines. Describe the purpose of each line.
39
108. What is a fair-lead?
109. Name four types of fair-leads.
110. What are rat guards and for what are they used?
111. What is a chain stopper and for what purpose is it used?
112. What is a heaving line? What is it used for?
113. How are masts supported?
114. What is a shroud and describe how it is used?
115. For what purpose are backstays used?
116. What are preventer stays?
117. What are bullropes and what are they used for?
118. What is a gantline?
119. What is the difference between a bull-rope and a gantline?
120. What is a Bos'n's chair and what is it used for?
121. Describe just how you would use a Bos'n's chair.
122. What is a stage?
123. Tell how you would rig a safe working stage.
124. What is a boat rope used for?
125. What is a pendant and for what is it used?
126. What is a bridle?
127. How is a bridle used?
128. What is a preventer guy?
129. Explain how you would rig an accommodation ladder.
130. What are the main oar commands and what do they imply?
131. What is meant by feathering an oar?
132. Why is it important that you cooperate in fire and lifeboat drills?
133. What is a station bill?
134. What gear should be attached to your lifesaving suit?
135. What is meant by two-blocking a fall?
136. How do you swing a boat into sea position using gripes and puddings?
137. How are boats on gravity davits launched?
138. How do you launch a boat in a seaway?
139. What are frapping lines and how are they used?
140. How do you rig a sea painter?
141. What is storm oil and how is it used?
142. Make a list of the equipment carried in a modern oar-propelled lifeboat.
143. What special equipment do motor
lifeboats carry in addition to regular lifeboat equipment ?
144. What comprises a first aid kit for lifeboat use?
145. How would you right a lifeboat that has been swamped in launching?
146. How do you rig a mast and sails on a lifeboat? Make a rough drawing illustrating this.
147. What provisions are carried for each person in a lifeboat?
148. How much water per person does a lifeboat carry?
149. What is a sea anchor ? How is it used?
150. How are signal mirrors used?
151. What is the abandon ship kit?
152. What are skates?
153. What are lifesaving nets? How are they rigged?
154. What is luminous marking?
155. What is the significance of remote control arrangement for main engines and pumps?
156. What is degaussing?
157. What personal equipment should you carry in a lifeboat?
158. What are the three main types of lifeboat davits?
159. How does the Liberty Ship davit differ from other types?
160. What is a cruciform bit?
161. What is the purpose of releasing gear?
162. What type of sail does the average lifeboat carry?
163. What are halyards?
164. What are sheets?
165. What lights are required to be carried by lifeboats?
166. How is a sea anchor hauled in?
167. What may be used in the place of a sea anchor ?
168. How do you treat sunburn?
169. What are pintals and gudgeons ?
170. What is a stern fast?
171. What are the parts of a sail?
172. How is a sail reefed ?
173. How many motor lifeboats are carried on ocean-going cargo vessels?
174. What are the duties of a lifeboat coxswain?
175. How are life rafts launched?
176. What equipment do life rafts carry?
177. How many life preservers do seagoing vessels carry?
178. How many life floats of the dough-type do seagoing vessels carry?
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179. When sailing, when would you say it is time to reef ?
180. Explain briefly the details of reefing.
181. When is a boom sail gybed?
182. How can you avoid gybing?
183. When should sheets be belayed?
184. What is a squall?
185. Would you keep the sails fuller in smooth or rough water?
186. What is a drag towed over the stern of the boat used for?
187. Do you reef around the sail or around the boom?
188. Is the sailing gear of a lifeboat suitable for heavy wind?
189. Will a heavily loaded lifeboat make more leeway than one lightly loaded?
190. What is a tanker?
191. How long does it take to load a tanker?
192. Explain briefly the various steps in preparing a tanker for a voyage.
193. Name and describe five classes of oils.
194. What is the difference between inflammable and combustible oil?
195. What are the proper signals to be displayed before starting the transfer of oil cargo?
196. Give five general safety precautions. Describe them.
197. How would you use a fresh-air breathing apparatus?
198. What is the difference between ventilation and venting?
199. Name two main principles involved in the cleaning of a tank.
200. What are two methods of cleaning cargo tanks? Explain each briefly.
201. Describe two methods of testing air in cargo tanks.
202. In which direction is a valve turned to close it?
203. Approximately how many turns are required to close a valve?
204. What is meant by "wetting down a ship ?"
205. When is the best time to wet down a ship?
206. At what speed do you think it is best to abandon ship ?
207. May a lifeboat be rowed through burning oil?
208. When should a life raft be released?
209. In which position should you jump from a ship ?
210. Describe the various swimming strokes which are most effective when swimming through oil-covered water.
211. What is a good method to stop paint working on the handle?
212. What is a manhelper and when is it used?
213. Name five articles which should not be painted on shipboard.
214. Should paint be put on in a thick or thin coat ? Why?
215. What is meant by binding a brush? What is the purpose of this?
216. How would you clean brushes after using?
217. How can you soften a brush that has become stiff ?
218. What is meant by boxing paint? Why is this done?
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TYPES OF SHIPS
The Maritime Commission has evolved four basic designs, vessels designed actually by American shippers and shipowners themselves. They are known as the C-1, C-2, C-3, and cargo-passenger - the C meaning cargo and the numeral the type. They were designed and later built in this order: 2, 3, cargo-passenger, and then 1. Non-standardized ships were also designed and built for special services. The greatest need in 1937 seemed to be representation in the North Atlantic passenger-carrying trade and the S.S. America, the largest and finest merchantman ever built in the United States, was the first vessel off the ways.
The great bulk and strength of the Merchant Marine, however, are the cargo carriers. In all the cargo types both steam and Diesels have been installed, depending upon the trade, fuel supply bases, and speed. The horsepower of each engine, installed in the same type hull, is always identical, shaft horsepower, propeller size and housing being standard. Between the horsepowers of 2,500 and 10,000 either steam or Diesel perform equally well, with steam performing more economically beyond 10,000. Practice indicates, however, that, hull for hull, Diesel is better suited for long routes and steam for routes of 3,000 miles or less.
The new merchant ships all have mechanical ventilation of the cargo holds. This eliminates sweating, a hazard to cargo-especially in the tropics-which has caused untold losses to shippers and high cargo insurance rates. It also removes one of the greatest hazards of the sea: fire. With forced ventilation below, spontaneous combustion is an unlikely happening. In order to save lighter-derrick charter or terminal crane services, the new ships are fitted with
5- and 10-ton cargo derricks. There are two to each hatch.
Crew quarters are now amidships and provide the finest seamen's living spaces on any ship of the world. Radio signaling and position-finding devices, the very highest forms of safety equipment, motor lifeboats, and compartmentation for flotation in the event of collision are all standard features.
For the first time in the history of the American Merchant Marine we have vessels which are above the minimum requirements of the Department of Commerce. All foreign trade interests had a hand in designing them and the completed ship represents the wisest compromise between what the American foreign trade requires and what it can afford. Cheapest insurance rates, maximum safety, speed but not a premium for speed, capacity, anti-spoilage provisions, economy of fuel and operating personnel, flexibility, ability to compete in any trade, and high living standards to attract American citizens as crew and passengers. That is the American merchant vessel of today.
One of the deficiencies of the merchant fleet was the lack of fast tankers able to stay with the battle fleet and make quick return voyages for refueling the fighting ships. They were the next ships to follow the S.S. America from the ways. Each is 553 feet long, 75 feet wide, and draws, loaded, 30 feet; each can carry 149,000 barrels or nearly 7,000,000 gallons of oil.
Especially designed for high speed, their trials were so satisfactory that the Navy immediately purchased most of them and they are now operating with the fleets. Those taken by private oil companies or operators were paid the difference between the cost of constructing
42
THE S.S. AMERICA, NOW THE U.S.S. WEST POINT
T-1 tanker and a slower speed ship which would have answered their needs. At any time the tankers may be requisitioned by the government and the base cost refunded.
The tanker hull is characterized by an enormous bulbous forefoot which materially provides stability and capacity without appreciably increasing resistance. On builders' trials the tankers bettered their designed speed by 2 knots an hour. Among other features originally designed for this class were magazine spaces, gun foundations, oiling-at-sea gear, heaving-lift facilities, and a flexible intertank pumping system permitting them to carry four or more grades of oil, discharge at will as much as desired, and reballast by pumping into dry tanks.
In normal times such a vessel would prove an able competitor in the foreign oil-carrying trade. At present her greatest use is as a naval auxiliary.
The C-2's 'are of two classes, steam-. and Diesel-propelled, with a common hull. They are 459 feet long, 63 feet beam, draw 26 feet, and log 15 1/2 knots sea speed. Tonnage, gross, is about 6,100 for each, displacement 13,900 and each has a bale cubic capacity of about a half a million cubic feet. Cruising range of the steam type is 13,000 miles and of the Diesel type 16,000 miles. Either type could cross the Pacific and return without refueling or make a round trip between New York and San Francisco and then cross the Atlantic on one bunkering.
The C-2's were the first of the new ships to
embody the raised standards of crew accommodations. All staterooms are for only two seamen or engineers and are equipped with wide berths, hot and cold running water, mirrors, reading and shaving lights, individual lockers, and are all outside rooms. Petty officers and crew each have their separate mess and recreation rooms with upholstered settees and individual tables for four. A dresser, drinking fountain, and library are provided and a steward's pantry is open twenty-fours a day for between-meal snacks and off-watch coffee, beer, and soft drinks.
Officers have private rooms, each with toilet and shower, as well as writing desks, wardrobes, and radio plug-ins. All living spaces are provided with ducts supplying heat or fresh-cooled air at will. Cooking is done entirely by electricity and meals are no longer the sketchy, unbalanced diets of the sea. C-2's as a standard feature, have accommodations for twelve passengers and thus serve as auxiliary passenger vessels in the colonial service.
The C-2 uses either one of two types of Diesel installation. One is a set of high-speed, two-cycle Diesels connected to the shaft by hydraulic clutches and gearing using a common bull gear. The other is a large single engine of the opposed piston type running at relatively low speed. Each type develops 6,000 shaft horsepower.
Both types use fresh water for cylinder cooling to ensure their long life, safe from the corrosive effects of salt-water cooling. In the dual
43
C-2 TYPE CARGO SHIP
installation the engines are directly reversible and both engines operate together normally. However, in case of breakdowns or during servicing at sea, one engine will still drive the vessel. Both types of Diesels use the same amount of fuel per hour, but the single engine uses a heavier and cheaper grade found the world over.
The steam-driven C-2's are equipped with turbine engines developing the standard 6,000 s.h.p. To reach this horsepower the steam is heated to 740 degrees Fahrenheit and is delivered to the engine at 440 pounds pressure. Boilers are paired, watertubed, and fired by oil under forced draft. Contract efficiency is 87 per cent, the highest efficiency requirement of any marine boiler afloat.
As a new departure in ship design, the boilers were installed in the same compartment as the engine. With this placement shorter steam leads are required and the officer on watch is able to observe all the main units from the operating station. Boilers are on an elevated flat, above the turbines, and this is possibly the first step toward completely integrated and self-contained power units.
All auxiliary machinery, including cargo winches, found on either the steam or Diesel C-2's is electrically driven. Main power is reserved exclusively for propelling purposes. The Diesel types make use of the exhaust heats to heat the vessel. A water-tube boiler is inserted in the exhaust line, which acts as a hot-water heating system and a muffler as well. In port,
with main engines idle, this unit can be fired by oil. The steam types have stand-by auxiliaries for heating and emergency power.
These two types of engines and installations have been the subject of much planning and inventing by American builders and designers. They are standard for all types of Maritime Commission ships and many private vessels. The old saying that a marine engine is useless without her engineer is passè. With standardization, any engineer officer is a specialist on all engines. He can jump from ship to ship as needed and be completely at home on his grading.
In the C-2's the ideal of balance of speed, cargo capacity, and economical operating characteristics has been attained. Trials have proved them among the most efficient and economical vessels in the world. Beyond all this stands out the great flexibility of arrangement and possible use. They may be very simply adopted for reefer service, for example-that is, the refrigerated hauling of beef, fruits, or other perishable cargoes-or for carrying heavy machinery, ore, or liquid cargoes. The C-2's have fulfilled the most urgent need of the Merchant Marine.
THE C-3'S
In answer to many requests the Maritime Commission has designed the C-3, a vessel of greater cargo capacity and speed than the C-2. These vessels are known as the C-3 general and the C-3 cargo-passenger. All are 492 feet long,
44
C-3 TYPE CARGO SHIP
70 feet breadth, and have a loaded draft of 28 feet six inches. Normal sea speed is 16y2 knots, though in practice this has been bettered. Gross tonnage of each is 7,680 tons, bale cubic capacity 684,000 cubic feet, and deadweight about 11,800 tons.
Propelling machinery is either steam turbine or Diesel with 8,500 shaft horsepower supplied by engines exactly like those of the C-2 but larger. The steam vessels have a cruising range of 13,500 miles and the oil-engined vessels, 15,500 miles.
It is essentially a freighter type but readily adaptable to specialized cargo or cargo-passenger combinations. She is a pretty ship, with raked stem and cruiser stern and shelter deck. Compartmentation and fireproofing requirements of Senate Report 184, which sets the highest standards of maritime safety known, have been met. The ships have five holds and seven watertight bulkheads carried to the shelter deck.
With slight changes, made at the request of lines wishing subsidies but not interested in outright cargo types, the C-3 became the C-3, cargo-passenger. She could now carry 100 passengers and 124 officers and men. The President Jackson was the first of the fleet, constructed, with government aid, for the American President Lines in round-the-world service. She was the first of ten C-3's to be fitted with the famous Bludworth direction finder, enabling her to navigate much as a plane does.
The second group of C-3's were in the South American trade for the Moore-McCormick Lines. They are Diesel-propelled and carry 217 passengers. The United States Lines altered the basic C-3 design for its specialized uses with
accommodations for 168 passengers and general cargo. The American South African Lines are using C-3's to carry 115 passengers. These are steam-driven and are the first of the newer ships to use all welded construction of the hull.
THE C-1'S
The smallest ships constructed to the Maritime Commission's designs are the most versatile of vessels. To some extent they replace the tramp steamer, being able to run economically the lesser trade routes which do not require excessive speed. They can be adopted for a variety of specialized uses, such as reefer ships, barreled oil carriers, general cargo or bulk cargo, and can accommodate eight passengers.
The C-1's are of two general types. each type propelled by either steam or Diesel as preferred by the operating company. The shelter deck type is 413 length by 60 feet beam by 23 feet draft. The Full Scantling type is exactly the same except that it is about five feet longer. All have shaft horsepowers of 4,000, cruise at 14 knots, and have cruising radii of about 10,000 miles. Accommodation standards are the same as for the C-2's.
On builders' trials the C-1's are consistently logging 16 knots, or about 15 per cent speedier than design and specifications call for. When these vessels become old, or after a long sea voyage has fouled the bottom, this extra power will enable them to maintain schedule speeds and arrivals.
THE SINGLE-SCREW TANKERS
The recognized need for large single-screw tankers with high speeds, in addition to the long-range, extreme-speed, twin-screw naval auxiliaries, led to the building of two of this
45
THE DEFENSE TWIN SCREW TANKER
type in two yards along the East Coast. These were for oil concerns who did not need a speed above 16 knots but were dissatisfied with the common tanker of 10 knots or less.
The single-screw tanker, known as the T-2, is 514 feet long with a breadth of 68 feet and draft of 30 feet. At 97 r.p.m. at the propeller, they develop 12,000 horsepower and cruise at 16 1/2 knots. Oil tank capacity is, 5,425,000 gallons in bulk, with tankage arranged for carrying and distributing (for ballasting purposes) several grades of oil.
These are ocean-going vessels and are not to be confused with the motor tanker commonly seen in the coastwise trade. A distinguishing mark of the T-2, though not exclusive with it, is that the main deckhouse and funnel is carried far aft. Otherwise, save for a flaying navigating bridge slighting forward of amidships, she is flush-decked and studded with oil gate valves, pumping hoses on short cranes, and a railed walk-around over the tanks themselves.
While it may seem the Maritime Commission has so standardized a vessel design as to rival the automobile assembly line, this is not the case. The design type is merely a basic design, the bulk of the engineering and research completed and, perhaps best of all, actual trials run and their lessons taught. Any shipping company with special requirements can still receive government subsidy loans through the Commission and have either a basic type altered to suit the peculiar needs of the company or have the Commission help the company's own architects design an entirely different vessel. The function of the Commission in such cases is to so control the design and construction that the provisions of the Merchant Marine Act are carried out. Its fundamental concern is that the vessel proposed is fit and worthy to take its
place in the American Merchant Marine and that it can be used as a naval auxiliary or as a replacement of a vessel taken for national defense or war uses.
Thus many existing ships were given government aid and altered and modernized to present Merchant Marine standards. These in no way outwardly resemble the various Commission types. In many cases the Maritime Commission was able to provide the basic design and with slight changes suit the shipping lines uses. The Maritime Commission had a vessel of which it officially approved and the shipper had a vessel which had been proved at sea and of which he knew the exact cost, speed, fuel consumption, and operating costs. Neither government nor owner was involved in costly and delaying experiments.
For example, the American Export Lines needed a fast freighter, to use steam but to have the range of a Diesel-propelled ship. The result was the C-3 Export, substantially a standard C-3 with additional bunker space and provision for refrigerating the cargo. In operation they have shown a steady, economical 16 1/2 knots.
When the Seas Shipping Company (The Robin Line) came to the Commission, their needs fitted best into the C-2 design. The Robin Line vessels have a slightly longer cruising range than the standard vessels and greater displacement and carry twelve passengers. Upper works have been somewhat streamlined and the characteristic cargo handling booms simplified. They have been called the "best-looking" freighters on the oceans.
The Mississippi Shipping Company, or Delta Line, received subsidies for the construction of combination passenger-cargo vessels for the Gulf Coast-South American routes. They carry
46
THE LIBERTY SHIP (OR EC)
sixty-three passengers instead of the twelve of the C-3, of which they are an adaptation, and have refrigerated holds to carry 9,000 cubic feet of reefer cargo. Because of the passenger-carrying features they were given a compartmentation of 2-plus, which means that more than two compartments may be flooded without causing the ship to sink, and are consequently exceptionally safe ships and ones which enjoy exceptionally low insurance rates.
One of the most interesting subsidies of the government is that given to the unique Sea Train Lines. This company operates a fleet of ships which, on four decks, each laid with standard-gauge railroad track, accommodates about one hundred loaded freight or tank cars. Cars are loaded, for example, in California, rolled to the Hoboken terminal, lifted aboard a Sea Train Lines, lifted back to land trackage in Havana, Cuba, and the goods finally delivered at a remote railroad siding in the interior of Cuba.
The freight car has become the package, saving the cost of many handlings, several packings, and, in the case of chemicals or liquids, expensive cooperage.
The Sea Train vessels are not unlike a tanker, being 480 feet long and 64 feet beam, with width enough for four tracks on each deck or nearly a mile in the entire ship. Seen at sea, it appears a modern, mildly streamlined ship, without sign of her cargo of railroad cars.
Private designs, while more numerous in the coastwise and intercoastal fleet, are to be found
in the foreign fleet as well. One of the most interesting is the combination cargo-passenger carrier of the Panama Railroad Company. These vessels are almost identical to the Maritime Commission's C-3, though they were developed and built several years in advance of this type.
THE LIBERTY SHIP (OR EC)
With the Army and Navy daily taking over the faster merchant ships under emergency conditions of national defense, The Maritime Commission has designed and ordered the Emergency-Cargo or so-called Liberty Ships. These vessels are as modern as the C's and are designed to replace those removed from the merchant service.
In order to speed up their delivery they are designed for only an 11-knot speed, which permits the use of reciprocating steam engines-an engine easily and quickly built and not requiring the high amount of machine work that the turbines or Diesels do.
The Liberty Ship is 425 feet long, 57 feet wide, and about 10,000 deadweight tons. They are all-welded hull construction and built to the same high standards as other Commission's vessels. In a sense they are the hasty emergency vessels of 1917, built fast and "by the mile." However, this time the United States had a wealth of engineering data, performance and operating records, and a fixed and sound program to assure an honest, sound, safe, and normal vessel and fleet.
47
SUBMARINE WARFARE
Since the first World War, the German submarine has improved considerably. The modern U-boat is reported to be able to dive to depths in excess of 500 feet and to be impervious to depth charges which would have destroyed her forerunner of 1918. On the surface a submarine presents a small and tough target for gunfire. The rounded surfaces and the thick plating of the pressure hull render the submarine immune to damage from machine guns and other small caliber fire. The conning tower has a very thick plating and has a watertight hatch at its base. Even a penetrating hit on the conning tower will probably fail to destroy the submarine, and it may fail even to interfere with her continued operation.
Damage to the upper part of the pressure hull of a submarine or to the control mechanism for diving prevents a submarine from submerging. If the submarine is unable to dive due to damage, and if she is far from her base and in waters controlled by the enemy, her eventual destruction by hostile air and surface ships is highly probable. A submarine confined to the surface, however, is not entirely defenseless. So long as the submarine retains her ability to use her guns and torpedoes, she is a dangerous vessel. It should be appreciated that not only are guns available to a submarine on the surface but torpedoes likewise can be fired from this as well as from the submerged positions.
A submarine which is undamaged does not normally remain on the surface to use her guns against heavily armed ships or aircraft. By doing so she accepts a needless risk and loses the submarine's greatest asset, the ability to
operate submerged and unseen. However, there are circumstances in which gunfire attacks will be made by the submarine. Gun shells are cheaper than torpedoes and there are more on board, as even the largest submarines carry only a limited number of torpedoes-perhaps no more than 32. Also at night a submarine, because of her small silhouette, can approach a large ship and open fire before being seen. She may even destroy her prey before being forced to submerge.
The gun battery of the German submarine consists of one or two guns of three and one-half inches or larger caliber, which would be effective against unarmored ships at ranges up to five miles, and two machine guns which are for attacks close aboard and against exposed personnel. German torpedoes are of two types. One is an air-driven torpedo having an effective range of about eight miles. The other is an electric and wakeless torpedo, which has a much shorter range of two miles. Both types of torpedoes can be fired when the submarine is either on the surface or submerged to periscope depth. Also, they can be fired on sound bearings with the submarine completely submerged to depths of greater than 100 feet.
One or two torpedo hits, if properly placed, will sink a large merchant vessel, although there are many instances of tankers and other ships which have come home after sustaining a torpedo attack from an enemy submarine (upper).
Submarines are equipped with very efficient under-water sound devices which permit them to discover the presence and bearing of large surface vessels within a range of five miles.
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This equipment also permits a submerged submarine to keep an accurate track of the position of attacking destroyers and other antisubmarine units. Evasive maneuvers are facilitated by the high maneuverability and the relatively small turning circle of the submarine. The German submarines are reputed to have made considerable progress in reducing the noise of their own machinery, and a submarine proceeding submerged at a speed of less than three knots is very difficult to pick up by even the best and most modern listening gear.
To destroy a modern submarine by means of depth charges the charge must be exploded very near the submarine's hull. To open up that hull a 100-pound depth charge must be exploded within 15 feet from the submarine. The lethal distance is somewhat greater with heavier charges, but in all cases in order to insure a kill the depth charge must be exploded close aboard.
Submarines can proceed on the surface at a speed of 18 knots or better. The submarine carries sufficient fuel to travel around the world. She also carries food and supplies for a cruise of several months' duration. Consequently, the German submarine operating along the American littoral does not need to be refueled or serviced by "mother ships."
There have been press reports that German submarines operating off the Atlantic seaboard have been refueled and have obtained supplies from disguised supply ships. While this is quite possible, the practice is much less general than is indicated by these press reports.
What definitely sends the submarine back home, if she is not sunk or damaged by her enemy, is the expenditure of her torpedoes. When the last bolt has been shot, she must return home to get a new supply. Torpedoes and the human factor determine the endurance of the submarine. This second factor, which may be easily overlooked by even seafaring men who are not accustomed to the cramped quarters of a submarine, is one of considerable importance. Submarine crews are likely to be tough and courageous, but under the continual stress of war conditions, unless frequently relieved and given comparatively long periods of rest and relaxation, their morale may show signs of deterioration. The loss of several famous U-boat captains who were an inspiration to the entire German submarine service has, no doubt, had its effect on the less experienced commanders.
When running submerged, a submarine has a maximum speed of about nine knots. Due to
the rapid exhaustion of the storage batteries at this speed, it can be maintained for only an hour or two. At lowest speed, two or three knots, the submarine can continue to cruise submerged for as much as two days, traveling as much as 100 miles during that time. By spending part of the time resting on the bottom, the submarine can remain submerged for as much as 60 hours. Because of the inherent necessity for submarines to surface, preferably at night or in thick weather, to charge their batteries, it is imperative to maintain for a considerable time a close watch on the general area in which the submarine has been seen to dive. This is particularly true when the dive has occurred early in the day. At that time she has obviously less chance of evading her pursuers than when she may be saved by the near approach of nightfall. When it is safe to do so, submarines prefer to remain on the surface, keeping their batteries fully charged for submerged attacks or for submerged escape. To fully recharge an exhausted battery requires about six hours on the surface, but one-half of any battery deficiency can be made up in about one and one-half hours. Usually, therefore, a period of one hour on the surface is enough to recharge batteries sufficiently to permit cruising submerged at slow speed for one day.
In making a daylight torpedo attack on a merchant vessel, the submarine usually approaches submerged, exposing the periscope at frequent intervals, for only a few seconds at each observation. Normally, because of the slow submerged speed of the submarine, the approach upon her target will be made well forward of the merchant ship's beam. The greater the speed of the merchant ship, the farther forward the submarine must be in order to initiate a successful approach. Because the submarine must make frequent and accurate observations and be fine upon the bow in order to be assured of a successful attack, the tactics of zigzag were adopted. This evasive principle frequently thwarts the submarine's plans; and when a zigzag plan has been prescribed, it is highly important that it be followed scrupulously.
Attacks are also frequently made at midnight and 0400, since these are the night hours when watches are in the process of changing, or when the eyes of newly established watch personnel remain unaccustomed to darkness. Since a period of 40 minutes is required to adjust the eye to darkness, this contingency may be avoided by overlapping watch personnel so as
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to maintain men on lookout who have undergone this adjustment.
Even in good visibility the merchant ship has small chance of seeing the brief exposures of the submarine's periscope or of detecting the submarine by listening devices before the torpedo has been dispatched. If, however, the merchant ship is screened by escort vessels equipped with good listening devices, the submarine must either accept a greater risk of detection or must fire torpedoes at a greater range, and consequently, with a smaller chance of hitting.
It must be borne in mind that the surface speed of the submarine is greater than the speed of all but the fastest of merchant ships. So, by proceeding on the surface outside of gun range, or outside of the visibility range of the merchant vessels, the submarine can frequently redispose herself so as to gain the position ahead to initiate either a submerged approach during good visibility or a surface approach during the hours of darkness. Good air coverage or fast, wide ranging, escort vessels, however, will make it hazardous for the submarine to attempt to overhaul her prey in this fashion.
In making night torpedo attacks, the submarine usually approaches on the surface, relying upon its small silhouette to permit an unseen approach to a firing position. The superior surface speed of the submarine will enable it to maneuver so as to take advantage of any special visibility conditions, such as moonlight, lighter sections of the sky near the horizon, or the glow of shore lights.
In torpedo attacks, either by day or night, the explosion of the torpedo is often the first notice of the ship being attacked. When a torpedo explosion is observed, it may be assumed that the submarine will be within a radius of 5,000 yards of the vessel-roughly on the beam and on the same side as the explosion. As pointed out above, the track of the torpedo is not always visible since many of the modern ones show little or no wake. When the submarine has launched her torpedoes from a shallow depth, the submarine may broach and the white swirl of her propellers become visible.
After firing her torpedoes the submarine ordinarily takes care to avoid exposing herself to gunfire from the damaged ship; remaining out of sight until her prey has foundered or taken such a list that her guns cannot be manned.
In rough weather the submarine will generally dive beam-on to the sea, altering her course
if necessary to reach this position. Normally she will surface head-on to the sea. Submarines forced to dive on account of air or surface attacks may alter course after diving. Furthermore, in order to confuse her assailant, a submarine may make a radical change of course just before diving.
There are many reports of the various colors and paint schemes of enemy submarines sighted by merchant marine personnel and other observers. It seems that there is no standardized technique employed. Bearing in mind, however, that the submarine commander is an individualist and usually an officer of considerable resource, it must be assumed that his ingenuity has extended to the point of improvising paints or other protective covering suitable to the area in which he is operating so that his vessel will assume as chameleonlike aspect as possible. On the whole, however, an over-all neutral tone that blends with the seascape is frequently used.
Very often the only proof of an object sighted being a submarine is that it unaccountably disappears. There has been one case during this war of a U-boat disguising herself with sails; a dummy funnel emitting smoke might also be used. There is also the possibility of a hunted U-boat firing a slow-speed torpedo, leaving a trace of oil, which may induce pursuers to follow a false scent.
When attacking unescorted ships in open waters a U-boat will probably endeavor to reach a position well ahead, unseen and on the surface. From here she will gauge her target's mean course. She will then dive fine on the bow, choosing her position from the point of view of light and sea. She will attack at an angle of roughly 90° from the target's course, firing one or more torpedoes at a range of 1,000 yards, or less.
When a convoy has an escort the above method would be risky. It is unlikely that an attack would be made on a single ship with an efficient escort unless that ship is known to be of very great value; but a convoy, so escorted, would probably be shadowed, the U-boat proceeding on the surface hull-down. She would then choose her line of attack so as to avoid contact with the escort as far as possible and would dive at high speed on a closing course.
If possible a U-boat does not fire a torpedo at a single ship when she is more than 1 1/2 points abaft the target's beam. The most dangerous arc is from 60° to 120° from right ahead. When the presence of screening vessels or the
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target's zigzag interfere with an attack, a U-boat may fire at a range of 1,500 yards and from a position up to two points abaft the beam. When attacking a convoy she might fire a "browning" shot, probably using a salvo of torpedoes, aimed at the convoy as a whole without singling out any particular ship, when the range may be over 4,000 yards.
When attacking single ships, German submarines endeavor, if possible, to close to a range of 500 to 800 yards to fire a torpedo. When attacking a convoy, they fire, if possible, at ranges between 500 to 1,000 yards.
At these ranges the torpedo runs at 35 to 40 knots (depending on the type), i. e., it runs 500 yards in 22 to 26 seconds.
It may be expected that longer ranges will be accepted if the target is screened by A/S vessels.
After an attack, one cannot say for certain just what tactics will be adopted. If the target is unescorted they will, as a rule, remain at periscope depth to watch the result of their attack. If an escort is present they will do their utmost to avoid the screening vessels. When the attack has been made at close range it is quite possible that a U-boat may continue diving at high speed and try to remain under a convoy. Normally, however, she will turn off her firing course, dive deep to about 250 feet and proceed at slow speed till the hunt has slackened.
This depends largely on conditions of wind, sea, and light, the number and positions of escorts and whether the target is zigzagging.
In bad weather a periscope is very hard to see, this is partly offset by the fact that the U-boat has to raise a considerable length of periscope to obtain clear vision above the waves. When at long range, as much as 2 feet 6 inches of periscope may be raised to enable details and course of the target to be obtained. As the range decreases the U-boat would show less periscope and, toward the end of the attack, she would possibly only show six inches in calm weather.
In the early stages of an attack a U-boat need not raise her periscope more than once every 5 minutes and then only for 5 to 10 seconds at a time; when nearing the firing position she will raise it every 4 or 5 minutes for not more than 2 seconds at a time.
A periscope cannot as a rule be picked up at a distance of more than 2,000 yards, even with good glasses. If, however, a U-boat is known to be on a certain bearing and weather and light
conditions are exceptional, it may be sighted up to 6,000 yards, with glasses.
All modern submarines have two periscopes and a good many have three, but, as a rule, only one of these is used at a time. Only one is fitted for use against aircraft.
At the commencement of an attack a thick periscope with high magnification is used to enable details of the ship and her course to be noted; in the final stages a thin attack-periscope showing a very small "feather" is used.
The number of night attacks, particularly on convoys and stragglers, has now increased considerably. Often a night attack will be carried out on the surface, but the optical qualities of U-boats' periscopes are very good and can be used in twilight and bright moonlight.
In any attack at night a U-boat would be guided by such considerations as position of escort, direction of the moon, and the afterglow of sunset, etc.
She would note carefully the tactics of the escort and run in on an avoiding course at high speed, fire her torpedoes and turn away, remaining on the surface, unless pursued by a fast hunting vessel-in this case she would dive deep and probably reduce to dead slow speed. If she were not hunted she might remain awash and reload her torpedo-tubes in readiness for another attack.
The worst condition for submarine operations is a calm sea, and if, in addition, there is a long swell running, it becomes almost impossible for a submarine to attack unseen.
At the other extreme, if the sea is rough, a submarine will become unmanageable when near the surface. If it is possible for her to make her final approach on a course at right angles to the direction of the sea, she may attack successfully in worse weather; but, unless she is thus favorably situated, she will probably give up any attempt to operate near the surface and will dive deep until the weather moderates.
The principal arc to be searched for U-boats is from right ahead to two points abaft the beam. Any U-boats sighted from right ahead to the bow would probably be at long range so the lookout on that arc should have binoculars if possible. The arcs between 4 and 10 points on either side require the most thorough search as it is there that a periscope or torpedo track is most likely to be sighted. When lookouts are double-banked one man on each side should use binoculars and the other should search for torpedo tracks and periscopes near the ship.
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HOW TO USE YOUR EYES AT NIGHT
OFFICE OF FACTS AND FIGURES
WASHINGTON
PRESS RELEASE
FOR RELEASE IN
MORNING PAPERS OF
SUNDAY, JUNE 14, 1942.
The Office of Facts and Figures today issued the following statement, calling attention to this example of an act of negligence that ended in tragedy:
The glow of a single cigarette at sea was the death warrant of a steamer, sunk by a German submarine.
This was revealed today in a broadcast by a German submarine captain to the German people from Radio Stuttgart. The broadcast was recorded by the Federal Communications Commission.
"The sea was calm, but the night was dark as we lay on the surface," the submarine commander said. "Our lookout on watch had no suspicion that a steamer was near until he saw the rise and fall of a spot of red in the distance. Strange as the light was out there in the lonesome sea, he recognized it as a burning cigaret and knew a ship was near. We trailed the ship for six hours and when dawn came torpedoed it."
The submarine officer explained that he satisfied his curiosity about the cigaret by questioning the survivors. He discovered that the cigaret was being smoked on the bridge, not by the sailor on watch, but by another who had dropped by for a chat and a breath of fresh
air, and was leaning on the rail and smoking.
Modern war is often war at night. That means that men must learn to use their eyes in new and unfamiliar ways.
This is written to tell you how to make the best use of your eyes at night. It will be of great help to you.
This material will not give you the uncanny eyes of an owl or a cat, but it may give you just the edge on the enemy you need to get in the first shot-and to get home.
WHAT HAPPENS WHEN YOU ENTER THE DARK
When you go into a dark room from a bright one it is hard to see until your eyes have become used to the gloom. At a movie it takes a minute or two to see the vacant seat. It may take another minute or two to be able to recognize a friend. During these minutes your eyes become much more sensitive to the faint light.
Your eyes adjust in two ways for seeing in the dark. As we have already seen, one way is by enlarging the pupil to let in more light or to make maximum use of what little light there is. Your eye pupils open wide in dim light and close to a pin-point opening when the light is very bright.
But this is not the most important change in the way your eye works in dim lighting. During the first half hour that you spend in dim light, the rods adapt to the dark; they become many times more sensitive than they were. This extreme sensitivity is retained as long as you stay out of the light and do not look at lighted objects. Whenever you look at light
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your night vision is damaged; the sensitivity is immediately lost, and your rods will have to dark adapt all over again.
NIGHT EYES ARE COLOR BLIND
The rod cells used by your night eyes are color blind. That explains the old saying, "all cats look gray at night." With your night eyes you couldn't tell the blue of a Navy uniform from the olive drab of the Army, or from the enemy's color. The uniforms would show up as different shades of grey but you would see no differences of color.
If you see a colored light shining at night, and it looks red or green or blue, it is only because it is bright enough so that you can see it with your daylight eyes. When you see the light with your night eyes, you see it as a light but not as a colored light.
RED LIGHT AT NIGHT
Your night vision is much more sensitive to light of some colors than to others. Your "night eyes" are no more sensitive to red light than are your "day eyes." Blue light, however, affects your night eyes about 1,000 times as much as it does your day eyes. To night eyes, a dim blue light will appear brighter and will be seen at a greater distance than a red light which is actually more intense. Lights of other colors come in between in visibility. For this reason, it is dangerous to use any light but red in a blackout, or on a ship, because it affects the enemy's eyes just as much as it does yours.
Night eyes lack the sharp vision for detail that your day eyes have. If you want to see to read, if you want to watch the dial of an instrument, if you must look at a map, a road sign, or your watch, then you must use your day vision. For this you must have good light -the more the better. Especially if the print or other forms are small, the light must be bright.
Red is the best light for this purpose. It is least likely to be seen by the enemy. But even a red light should not be exposed or directed toward the sky. A red light, bright enough to read by, can be seen at a considerable distance by the enemy if the light itself is not shielded from his direct view. The reflection from a red flashlight on a map or an instrument or whatever you are looking at is not so likely to be observed. The enemy's night eyes can see the reflection of a yellow, green, blue or white flashlight from a much greater distance than the reflection of a red light.
It is clear that you cannot afford to be careless in exposing a red light where the enemy might see it directly. Red has less chance of being picked up by the enemy than blue. But if it is seen at all it provides a better target. Red is sharp and clear, blue is fuzzy.
Night eyes are extraordinarily sensitive to faint light. This is shown by calculations that an ordinary candle flame could be seen at a distance of more than 10 miles if the night were completely black, and if haze and dust did not interfere. A lighted match is about as bright as a candle flame. Under ordinary night conditions a match can be seen from a plane several miles away, and a lighted cigarette is known to have given away the position of a ship to an enemy submarine.
GAINED IN AN HOUR-LOST IN A MINUTE
When you step from a brightly-lighted room into the dark outdoors, you are practically blind at first. Then several things happen. First the pupil of your eye dilates, letting more light into your eyes. This is a mechanical action. Next the cones of your day vision adapt to the darkness. This takes about five minutes and after that you feel more comfortable about moving around in the dim light.
After a much longer time your rod vision adapts itself to the darkness and you begin to see shapes and outlines in the gloom that were not even vague bulking shadows when you first went into the darkness. Complete dark adaptation takes nearly an hour but most of this is accomplished at the end of the first half hour.
Just how this change-over from your use of cone to rod cells is accomplished is not completely understood but it is at least partly a chemical process.
The man who, at a command or an alert signal, leaves a lighted room to run on duty without having prepared his eyes is completely at the mercy of the enemy so far as his vision is concerned. By the time he gains the use of his night eyes the emergency may be all over.
And even when your eyes are adapted to the dark, flashing on a light, even for a very short time, or striking a match to light a cigarette, may ruin your night vision for another half hour. You can lose in a few minutes all you gained by half an hour in the dark. The brighter the light and the longer you look at it, the more you lose.
GETTING YOUR EYES READY
Complete darkness is the best preparation for
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night fighting or night lookout. It pays to protect your eyes from light before you start and while you are out. If you can't stay in darkness, keep the lights around you as low as possible and don't look straight at them. If it is necessary to look at any lighted object, be as quick as you can about it. Experiments have shown that looking at an instrument dial lighted only by radium paint will cut down the distance at which you can see a friendly or an enemy plane by fifty per cent. Don't look at the dial any longer than you must or the loss will be greater.
Experienced gun pointers and spotters know that they must not watch the flash of their guns as they fire. The flash of a six-inch gun may dull your eyes for a minute or more. Under continuous fire at dawn or dusk it is impossible to aim some rapid-fire guns accurately at a target more than seven times a minute if the gunners watch the flash. At night the blinding effect would be even greater. Looking away from the flash gives almost complete protection. Luckily the flash of rifles and small-caliber machine guns has very little effect on the eyes. If you are to go on night lookout duty, remember that the safety of the ship and of every member of the crew depends on your ability to use your night eyes. Any light you look at, even for a moment, during your watch, or for a half hour before, will allow the enemy to come closer for his deadly shot, before you are able to detect and report his presence.
SUBSTITUTES FOR DARKNESS
There are several ways by which you can become dark adapted or keep your dark adaptation even though you must work in fairly bright light. Each way is suitable only for certain kinds of jobs.
Ship pilots and bridge officers have long known a clever but simple trick. When they have to work their way through dark islands, when beacons are unlit, or when moving in company with blacked-out ships, these men often have to go back and forth from a lookout post to a lighted bridge or chartroom.
When they go into the light they cover one eye.
Then, when they look out into the night they uncover this eye and use it. To cover the eye an ordinary black eye patch is sometimes used. This trick should not be used, however, to prepare for watch except in an emergency. Experienced men who do night watch know that
they must get out of the light for about 15 minutes to half an hour before they go on duty. With the patch over but one eye, only that eye becomes prepared, and two eyes are better than one.
USE OF RED LIGHT
A better way to get the eyes dark adapted is to work in deep red light. Remember that red has less effect than any other color on the rod cells of your night eyes. So if red light is available, you can read or work if you have to, and still be dark adapting your night eyes, so that you will be ready for nearly instant action in the dark. If dark red bulbs aren't available, a deep red cellophane covering for a light or instrument will help. Red cellophane is not as good as a red bulb since it lets through some orange and white light, but it will help in a pinch. Even with red light, however, you should be careful not to use any more light than you need. Too much light will spoil dark adaptation even though it is red.
Tight-fitting goggles with red lenses are an excellent way to protect the eyes for dark adaptation. If you can obtain them, wear them for half an hour before your duty begins.
The use of red light or red goggles makes it impossible to see red lines on charts. Lines of this color look white under red light, so that they cannot be seen on a white map or chart. In the same way, red signal lights look the same as white when goggles are worn. Be careful not to mistake one color for another when you are working in red light or wearing red goggles.
LEARN HOW YOUR NIGHT EYES WORK
Learning the most effective use of your eyes at night is like learning to use a precision instrument. Practice is necessary in order to acquire the ability you need. There are some games or tricks which depend on skill in night vision. If you learn to outwit your friends with these tricks you may later win higher stakes in night battle with the enemy. Here is one experiment:
No elaborate preparation is needed, but you must be able to darken your room until it is blacked out.
First have a sheet of typewriter paper. Tear or cut this in two in the middle, crosswise. Then cut one of the halves in two, repeating with one of each pair until the smallest scrap is only about a quarter-inch across.
Now spread the pieces in order of size across a black card table or other dark surface. Then
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keep your eyes on the smallest piece of paper while you darken the room until that piece drops from sight.
Now run your eye along the row. You'll see that the paper sheets seem to grow brighter with size. The biggest piece may even seem to glow. But watch the biggest piece ! While you look steadily at it, it will seem to fade. And if you notice the whole array of pieces with the tail of your eye, you may be surprised to find that the smallest ones that were dimmed out while you looked at them have now popped out like stars "coming out" to shine in early evening. If you look at them again they will disappear.
This is a dramatic sort of experiment. It seems mysterious, but is easily explained. The very center of your eye which has no rods, is "blind" when you are using your night eyes. You will not be able to spot an airplane overhead if your eyes are directed right at it. You can pick it up by using the angle of night vision which you discovered in your experiment. But it will disappear if you look straight at it. The same thing is true if you try to see a distant ship, an unlighted car or tank, or even a man on a dark night.
Always remember that you must look a little to one side in order to see best on a very dark night. Learn to pay attention to things which are just a little off to the side. Learn to keep from looking directly at any object. As you feel your eyes drawn irresistibly toward what you want to see, just let them slide on over it to the other side and look again with the tail of your eye. It takes practice to learn to do this without fail, but it is worth the trouble to learn the trick.
And don't keep looking steadily to the same side of an object. This will make it disappear too, because you will be fatiguing the rods which you are using. Shift your gaze frequently. Every time you do this you will be using rested rods which can do a better job of seeing, and the ones that you were just using will then be given a chance to rest.
Another simple experiment can be done as follows:
After you have been in your darkened room or outdoors for about 15 minutes, hold up your finger and look steadily at it. It will disappear. Look a little to one side and it will appear again. But if you keep staring at this side it will soon be gone again. Move your eyes to the other side and back it will pop.
In night watching don't try to sweep your eyes over the sky or the horizon-you can't see well while the eyes are moving. "Scan" the sky, don't sweep over it. Night eyes are slow in responding. At night a faint object may not be recognizable until after you have looked near it a number of times. If you ever hunted quail in the morning or watched deer in the dusk, you know that you can look right at the object without noticing it. In darkness it is even harder to pick out because you won't see it at all if you stare. You have to look again and again at points near it.
SMALL THINGS ARE HARD TO SEE AT NIGHT
Small objects cannot be seen with your night eyes. The average airplane becomes too small to be seen beyond 1,000 feet on a clear, starry night. It is visible that far away only if you are directly above or below it. The plane looks smaller when seen from straight behind, or ahead, or from the side. It cannot be seen further than about 400 or 500 feet from these angles. If you are pursuing a plane, try to keep above or below it until you close in. The same thing should be done if you are chasing a boat. Keep off to one side when far away, if you can, so that you see the boat more nearly broadside on.
Night glasses are useful because they magnify an object. Ordinary binoculars do this too, but binoculars cut down the amount of light that gets to the eye. Night glasses magnify without sacrifice of light. They don't give a clear, sharp view, as binoculars do, but at night we can't get a clear, sharp view anyway. By magnification, the night glasses make it possible to see objects or parts of objects that would otherwise be too small to be seen at all. Thus they help to identify objects which have already been spotted.
Darkness not only makes it hard to see things, but it also changes the appearance and apparent size of objects when we do see them. A tree seen against the night sky looks much smaller than in the daytime because the twigs at the ends of the branches can't be seen at all. And for the same reason an airplane caught in the beam of a searchlight looks larger than the same plane seen as a black mass against a dimly-lighted sky.
Darkness blots out details on which we have learned to depend for identification, perhaps without quite realizing it. You know how hard
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it is to recognize a friend from a silhouette cut from black paper. It may be just as hard to identify a plane or ship from the solid black form that is visible at night.
SEEING THE INVISIBLE
Recognition even in the daytime is usually a matter of jumping to conclusions from slight hints. You are able to recognize a friend long before you are close enough to him to see the color of his eyes or the width of his mouth.
At night, you have to be able to work on even smaller cues. It will pay you to study silhouettes of the ships, tanks, or planes you will need to recognize with this in mind. What distinguishing marks are easiest to make out in the darkness ? How can you tell a periscope from a buoy?
Anything in motion is easier to see. That is why a soldier freezes when he doesn't want to be seen.
Sometimes you may be able to detect a moving airplane in the sky by its motion alone rather than by its form. Sometimes you have to rely on what you don't see, more than on what you do see. If stars suddenly blink out and on again, you know that something has been in the way.
CONTRAST HELPS NIGHT VISION
One thing that helps your vision both at night and during the day, is the contrast between an object and the background.
If the thing observed is very different from its background, it is much more readily seen than when the object and its background are quite similar. Similarity of object and background, as a protection against visibility to the enemy, is quite evident with animals and birds. The white polar bear is much less visible against a background of white snow, the chameleon even changes his color to correspond with his background.
In warfare, one must reduce the contrast between himself and his background, and he must discover ways to increase the contrast between the enemy and his background.
An airplane (which is dark) may be easily seen if you look up at it against the night sky, but it may be invisible if you look down on it against the dark ground. A ship may show up clearly against the starlit sky and even more clearly against a coast that is not thoroughly blacked out; but the ship may fade into the background if you are looking at it against dark
water. If light from the moon is reflected onto the under side of an airplane from white clouds below it, the plane may become as bright as the sky behind it, and this lack of contrast against the sky may make it invisible.
To notice small differences in contrast, it is essential to have clear vision. It is for this reason that windshields must be kept clean and free from scratches or fog. These tend to scatter light in all directions and reduce contrast. Careless night fighters have been known to tolerate enough dirt on their windshields to double the time it takes to see a plane moving along near by. And sailors on ships sometimes let the salt from spray pile up in blotches on the glass. This is courting death.
For the same reason it is important to keep down the lights on your side of a windshield. Any light on your side reduces the contrast because stray light spreads over the whole glass and reflects in your eyes. That is why you push up close to a window when you try to look out at night. By coming up close you shade part of the glass and increase the contrast of the objects seen through this part. If it is necessary to have any light on your side, keep it as dim as you can and screen it from the glass. This also helps your dark adaptation.
PRACTICE
It is not enough to know how to use your eyes correctly at night. When you learn to drive a car or steer a ship you must practice doing it. In learning to use your eyes at night, actual practice in doing it is absolutely necessary. Here are two games that will help you gain this practice:
SPOTTING GAME
Any number can play. One player should scatter little bits of white paper over a dark table in an almost completely dark room. (If you have time, cut tiny airplane silhouettes in various small sizes from white paper.)
In succession, have each player count the "planes." Then turn on the light and check the score.
How to win. 1. Try to be last to count, so as to have your own eyes dark adapted. 2. Let your eyes move about and try to catch the "planes" with the tail of your eye. 3. If you think you spot one, don't look directly at it to make sure. Look first to one side, then to the other of where you think it is. 4. Play your hunches. If you think you see one, but are not sure, count it.
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When the bright light has been on for about five minutes, turn it off for:
TARGET PRACTICE GAME
Each player must have a different colored pencil. A hit is registered by putting a dot or cross in the exact center (if possible) of each "plane." Use the same cut-outs you used for the spotting game. If you like you can have them marked with bull's eyes, with lowest score for the outer circle on the biggest plane-highest score for the center on the smallest plane.
How to win. Protect your eyes from the light while it is on and from all bright surfaces. Be sure not to look directly at the plane when you "shoot." Shoot quickly-if you hesitate, you may unintentionally look at what you are shooting and "lose" it. With practice and experiment you can develop other tricks to help your score. If you do, these same tricks may mean victory on some dark moonless night on duty.
VITAMINS
There has been a good deal of talk about the effect of shortages of vitamins on ability to see at night. These are the vitamins in fresh vegetables, butter, cream, cheese, liver and fruit. People who don't get enough of these vitamins do become poor in night vision. Extra vitamins don't improve night vision if your diet or your night vision is already normal.
FITNESS
Night vision is affected by fatigue. Anything that reduces your physical well-being has
a greater effect on night vision than on day vision. Experiments have shown that hangovers, slight illnesses, not using enough oxygen in flying, or excessive fatigue may double or even triple the amount of light needed to see an object.
The night fighter must train for his job as a boxer trains for a big match. The boxer who is not at the peak of training is likely to be knocked out. The night fighter whose eyes are not at the peak of efficiency is likely to be killed.
REMEMBER THESE THINGS
(1) Protect your eyes from light before you go on night duty and while you are out.
(2) Don't look directly at any light or illuminated object. If you must, be quick about it.
(3) Use the corners of your eyes. Night targets are more clearly seen when you don't look directly at them.
(4) Keep your eyes moving. Quick, jerky movements and short pauses are better than long sweeping movements and long pauses.
(5) Keep yourself wide awake and on the alert. Don't break training. Use good sense about eating, drinking and smoking.
(6) Practice what you know about seeing at night until it becomes second nature to use your eyes to the best advantage. Use every possible device to aid you in learning to recognize ships, planes and other important objects from slight cues.
