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MANUAL FOR

EXPENDABLE RADIO SONO-BUOY

TRAINING RECORDS

 

Prepared by
Columbia University - Division of War Research
at the
U.S. Navy Underwater Sound Laboratory
Fort Trumbull, New London, Connecticut


Distributed by

U.S. NAVY
Bureau of Aeronautics
Special Devices Division

 


Drawing of the 78 record lables:
U.S. Navy, Bureau of Aeronautics - Special Devices Division
Device 15P3
Expendable Radio-Sono-Buoy Training Records
1. Introduction To Submarine Sounds
Examples
1. Water Noises, 2. Propellor Beats, 3. Machinery sounds, 4. Auxillary motor sounds, 5. Propeller beats and machinery sounds together.
78 RPM OUTSIDE START
Prepared by Columbia University, Division of War Research at the U.S. Navy Underwater Sound Laboratory, Fort Trumball, New London Conn.

USE OF STROBOSCOPIC PATTERN
TO SET YOUR PHONOGRAPH AT 78 R.P.M. --

Place the training record on the turntable and turn on the phonograph. Look at the stroboscopic pattern on the outer edge of the label, under a single A.C. light. If the light is 60 cycles, look at the inner pattern of squares; if the light is 50 cycles, look at the outer pattern. In either case, the stroboscopic pattern will appear to be standing still if the turntable is at the correct speed of 78 RPM. If the pattern appears to be traveling forward (in the direction the record is turning), the turntable is turning too rapidly; if the pattern appears to be traveling backward, the turntable is turning too slowly. Adjustments of the speed should be made while the turntable is revolving.


EXPENDABLE RADIO SONO-BUOY
TRAINING RECORDS

Drawing of record with images of ships and fish sounds coming out.

THE RECORDS and WHAT THEY CONTAIN
I. Introduction to Submarine Sounds (1) Water noise
(2) Propeller beats
(3) Machinery sounds
(4) Auxiliary motor sounds
(5) Propeller beats and machinery sounds together
II. Cavitation: Effect of Depth and Speed (Fleet Type Submarine) (1) Periscope depth, 7 knots
(2) Periscope depth, 3 knots
(3) Periscope depth, 6 knots
(4) 250 ft. depth, 6 knots
(5) 250 ft. depth, 8 knots
III. Cavitation: Effect of Depth , and Speed (Old Type Submarine) (1) Periscope depth, 3 knots
(2) 100 ft. depth, 3 knots
(3) Periscope depth, 2 1/2 knots
(4) 100 ft. depth, 2 1/2 knots

[1]


IV. Estimation of Submarine's Speed by Counting RPM (1) Fleet type submarine, 120 RPM, 6 knots
(2) Old type submarine, 150 RPM, 3 knots
(3) Fleet type submarine, 140 RPM, 7 knots
V. Effect of Underwater Range on Submarine Sounds (1) Range - 200 yards
(2) Range - 1,000 yards
(3) Range - 200 yards
(4) Range - 1,000 yards
(5) Range - 300 yards
VI. Comparison Between Sounds Produced by Surfaced and Submerged Submarine (1) Periscope depth, 3 knots
(2) On surface, 7 knots
(3) Periscope depth, 3 knots
(4) Blowing tanks and surfacing
VII. Interfering Sounds: Submarine and Destroyer Escort (1) Submarine, periscope depth, 3 knots
(2) DE, 15 knots
(3) Submarine, 500 yards; and DE, 1500 yards
(4) Submarine, periscope depth, 5 knots; DE, 10 knots, approaching from 1,000 yards
VIII. Sounds Produced by Activities Aboard Submarine (1) Operating trim pump
(2) Bleeding down ballast tanks
(3) Operating radar-training motor-generator
(4) Pounding on pipes and bulkhead
(5) Operating torpedo data computer
(6) Slamming bulkhead door
(7) Announcing over P.A. system, shouting of crew
(8) Sounding alarms
(9) Charging batteries

[2]


IX. Marine Life Sounds (1) Croakers
(2) Black drumfish
(3) Snapping shrimp
(4) Garibaldi
(5) Porpoises
X. Surface Craft Sounds (1) Surf Landing Boat, 15 knots
(2) Cruiser, 9 knots
(3) Destroyer, 14 knots
(4) Battleship, 7 knots
(5) Freighter, 8 knots
(6) Destroyer Escort, 15 knots
XI. Torpedo, Minesweeper, and Foxer Sounds (1) German electric torpedo
(2) German air torpedo
(3) Acoustic minesweeper
(4) Foxer
XII. Depth Charge Explosions (1) Range-2 miles
(2) Range-1 mile
(3) Range-1,000 yards
(4) Range-100 yards
(5) Depth charges as heard aboard submarine
XIII. Identification Test Nine examples to be identified (See page 11 for answers)
XIV. Identification and Turncount Test Six examples to be identified and one example for turncount test (see page 11 for answers)
XV. Search Problem Three buoy pattern (See page 12 for answers)
XVI. Search Problem Five buoy pattern (See page 13 for answers)
XVII. Search Problem Five buoy pattern (See page 14 for answers)
XVIII. Search Problem Five buoy pattern (See page 15 for answers)

[3]


Drawing of two woman stick figures with records as heads trying to lure a sailor.

HOW TO USE THE RECORDS

The ERSB Training Records have been prepared to help you teach the use of the Expendable Buoy. They describe and explain most of the important sounds your students must recognize.

Useful as they are, the records are not a whole training program by themselves. They should be used together with lectures, demonstrations, slide films, and other teaching devices, to make up an effective, well-rounded course. Although the records are• in logical order, they may be used independently of each other, if necessary, to fit into your training program.

Don't play too many records at one time. Your class will get bored. It's a good idea to study the contents of each record in advance, and then spot the records in your teaching program where they will do the most good. The records should reinforce and review material that you have already given in lectures.

If used carefully, the training records will do a considerable share of the teaching job and will also add variety to the training program.

[4]


Drawing of a record with three sailors trying to figure out what to do.

MORE ABOUT THE RECORD CONTENT

On the first pages of this booklet, the content of each training record was briefly indicated. Additional information about the records is given below. Complete scripts for the records are given beginning on page 16.

RECORD I - Introduction to Submarine Sounds

This record is designed to acquaint the student with the chief sounds produced by a submarine-propeller beats, machinery sounds, and auxiliary motor sounds. Examples of these sounds and a general explanation of submarine sounds are given. An example of water noise is also included since a major part of submarine detection depends upon the operator's ability to distinguish submarine sounds from the background water noise.

The submarine sounds on this record were recorded over the buoy equipment from the USS BLUEGILL, an American fleet type submarine.

[5]


RECORD II - Cavitation: Effect of Depth and Speed (Fleet Type Submarine)

RECORD III - Cavitation: Effect of Depth and Speed (Old Type Submarine)

These two records explain how propeller beats are produced by CAVITATION. Cavitation depends mainly upon the speed and depth of the submarine. However, other factors, such as the size and shape of the propellers, the condition of the blades, and the thrust of the propellers also affect cavitation.

The following chart shows the approximate speeds at which cavitation begins for our fleet type submarines, for our older, smaller type submarines, and for the captured 500 ton German submarine "GRAF." Speeds are given for several depths. This data was obtained from only a few examples, so it may not be strictly true for all submarines.

Speed at Onset of Cavitation

Depth American Submarine
Fleet Type
Knots
American Submarine
Old Type (S-20)
Knots
German
Submarine Graf
Knots
Periscope 3.5-4.0 2.5-3.0 3.0-3.5
100 ft. 4.0-4.75 3.0-3.75 3.5-4.0
150 ft. 4.75-5.5 3.75-4.5 4.0-4.5
200 ft. 5.5-6.25 4.5-5.0 4.5-5.0
250 ft. 6.0-7.0 5.0-5.5 5.0-5.5

RECORD IV - Estimation of Submarine's Speed by Counting RPM

This record explains why and how to count a submarine's propeller beats.

When propeller beats are heard, they usually correspond to the revolutions of the propeller shaft. That is, for each propeller beat, the shaft is making one complete revolution: Sometimes, you may hear the beat of each blade. But usually one of these beats will predominate to the extent that a shaft count can be obtained.

[6]


To determine the RPM, it isn't necessary to count the beats for a 1-minute period. The beats can be counted for a shorter time and then the figure can be multiplied to give the correct REVOLUTIONS PER MINUTE. For example, the propeller beats can be counted for 30 seconds, and the count can then be multiplied by 2 for the correct RPM; or the beats can be counted for 15 seconds and the count can be multiplied by 4, and so on.

The RPM per knot varies for different submarines. Our fleet type submarines make about 20 RPM per knot; our older smaller type make between 40 and 50 RPM per knot; the German sub GRAF (a 500 ton type) makes about 37 1/2 RPM per knot. In any case, however, if the RPM of a submarine is known, and the RPM per knot is also known, the speed of the submarine can be found by dividing the RPM by the RPM per knot.

Speed = RPM / RPM per knot

RECORD V - Effect of Underwater Range on Submarine Sounds

The range or distance a submarine can be detected by the Expendable Buoy depends upon the amount of noise produced by the submarine and upon water conditions. Some submarines are inherently noisier than others, and as any submarine increases speed, it produces more noise. The condition of the water is the other factor affecting range. Temperature gradients, salinity, particles of foreign material in the water, and the state of the sea will each affect the range of underwater sound.

A quiet sub, running at slow speed and under very adverse water conditions may be detectable only within a few hundred yards of the buoy. On the other hand, a noisier sub at high speed, under excellent water conditions, may be detected at a distance of, several miles. A DE, under good listening conditions, has been detected at

[7]


a distance of more than 10 miles. Acoustic minesweepers have been picked up at 20 to 30 miles.

Naturally, as a submarine comes closer to the buoy, its signal will become stronger and more pronounced as compared with the water noise. There will be a better signal-to-noise ratio, and not merely a general increase in volume such as you would get with a higher volume setting.

In the examples used on this record to demonstrate range effect, the submarine was within a few hundred yards in the "close" examples and over 1,000 yards away in the "distant" examples. The first three examples are recordings of the USS BLUEGILL and the last two examples are recordings of the USS PINTADO, both modern fleet - type submarines.

RECORD VI - Comparison Between Sounds Produced by Surfaced and Submerged Submarine

In a "gambit," or ''baiting," maneuver, your attacking plane retires from the submarine's area and waits for the submarine to surface. By listening carefully for any change in the sub signal, you may have a good indication that the sub has surfaced. This can be checked with radar before proceeding with operations.

In the surfacing example on this record, the squeaking sounds heard after the sub has surfaced were caused by hand operation of valves controlling the ballast tanks.

RECORD VII - Interfering Sounds: Submarine and Destroyer Escort

This record teaches the student to differentiate between the sound of a DE and the sound of a submarine when the two are heard together. In a real attack, the submarine signal may be completely drowned out by the sound of the DE. If the DE also loses contact with the submarine, she may have to withdraw from the area until the plane can again pick up the sub's signal.

[8]


In the last example on this record, the speed of the DE is 10 knots, which is the usual speed for an ahead thrown attack. If the DE were making a 15 knot speed as in a conventional depth charge attack, the submarine signal would have been more completely masked by the sounds from the DE.

The DE in the examples was of the 1720 ton class, and the sub was the USS S-20, which was constructed in 1920.

RECORD VIII - Sounds Produced by Activities Aboard Submarine

The miscellaneous noises aboard a submarine probably will not be heard over the buoy equipment unless the submarine is very close to the buoy (under 100 yards). The examples in this record were obtained over a hydrophone located 50 feet from the conning tower of the submarine USS CAVALLA.

RECORD IX - Marine Life Sounds

There are many species of marine life that produce sounds. This record contains examples of a few of these sounds.

If you hear sounds which lack rhythm or continuity, they are probably caused by fish or marine animals. If the sounds are regular in pattern, or continuous, they are probably man-made.

RECORD X -Surface Craft Sounds

Large surface craft create considerable underwater noise, which may be picked up many miles away. Since many surface craft sound somewhat like submarines, a careful study should be made of the sounds on this record so that slight differences in character may be observed.

[9]


Following are the speeds of the several ships heard:
Surf Landing Boat 15 knots
Cruiser 9 knots
Destroyer 14 knots
Battleship 7 knots
Freighter 8 knots
DE 15 knots

RECORD XI - Torpedo, Minesweeper, and Foxer Sounds

The staccato roar of a torpedo, the stuttering of a minesweeper, and the buzz of a Foxer can easily be distinguished from the comparatively slow propeller beats of a submarine or surface craft. The torpedo, minesweeper, and Foxer put out very strong signals which can be picked up many miles away.

RECORD XII - Depth Charge Explosions

The depth charges heard over the buoy on this record were Mark 47's dropped from an airplane and set to explode at a depth of 25 feet. The distance of the explosions from the buoy in each case was 2 miles, 1 mile, 1000 yards, and 100 yards respectively. The explosions appear to be equally loud regardless of the range, because each is strong enough to overload the receiver.

The sounds from each explosion last about 15 to 20 seconds. Explosion sounds sometimes last as long as 50 to 60 seconds.

RECORD XIII - Identification Test

RECORD XIV - Identification and Turncount Test

These are test records containing 16 sounds to identify and one turncount problem. The tests are not only a check of the student's ability to recognize underwater sounds, but also serve as a review of the sounds. The class should be equipped with writing materials, and each student should be directed to write his answers as specifically

[10]


as possible. For example, if he thinks he hears the propeller beats of a submarine, he should write, "Prop beats of submarine." If he thinks he hears machinery sounds and auxiliary sounds of a submarine, he should write, "Machinery sounds and auxiliary sounds of submarine," and so on. At the end of each test record, the instructor should give the correct answers and encourage discussion of the sounds heard.

Answers for Record XIII are as follows:

1. Water noise only
2. Submarine propeller beats (or) submarine propeller beats and machinery whine
3. Machinery whine from submarine
4. Water noise only
5. Submarine's auxiliary motors (bow and stern planes)
6. Minesweeper
7. Sub propeller beats and machinery whine
8. Croakers
9. Submarine charging batteries
10. Submarine propeller beats and depth charge

Answers for Record XIV are as follows:

1. Submarine propeller beats (or) submarine propeller beats and machinery whine
2. Water noise only
3. Submarine propeller beats and minesweeper
4. Surfaced submarine running on Diesels
5. Destroyer Escort, 15 knots
6. Depth charge
7. RPM-120, Speed-6 knots

[11]


RECORDS XV, XVI, XVII, and XVIII-Search Problems

These records contain problems which simulate the sounds which might be heard when a pattern of buoys is dropped.

Before these problem records are played, the class should be equipped with writing materials, and each student should understand the pattern to be used. Also, it is suggested that he indicate the position of the submarine in his solutions with an "S." To assist the student to locate the submarine, he should indicate, beside each buoy on his pattern, the relative strength of the signal received. If a submarine signal is weak on the Purple buoy and strong on the Blue buoy, he should write "weak sub" and "strong sub" beside the respective buoys on his pattern.

Record XV assumes that 3 buoys have been laid out as a right triangle, with the Purple buoy at the lower left or center position, Orange at North and Blue at East. It should be, emphasized that in actual practice the final pattern is dependent upon the sounds picked up over the buoys. For example, in Record XV, if a sub signal were heard on the Orange buoy it would become the center buoy of the pattern and you would probably proceed to drop the Blue buoy in a more distant northerly position instead of at East.

In Record XV, a modern type sub is heard over the Purple and Blue buoys. Only water noise is heard over the Orange buoy. Notice that in the diagram, notes have been made for the first round of listening, then crossed out and replaced by notes for the second round.

PATTERN FOR RECORD XV

Orange, Purple and Blue are arranged as a right triangle with O on top. The submarine is below Purple and Blue between the Purple and Blue.

[12]


Record XVI assumes that 5 buoys have been dropped in a conventional pattern. On some of the buoys only water noise is heard, on others the submarine is heard with varying degrees of intensity.

During the first part of the problem, propeller beats are heard on the Purple, Red, and Yellow frequencies. The loudest signal is heard on the Red frequency.

On the next round of listening the sub is heard only on the Red frequency. Evidently the sub is close to the Red buoy but going away from the pattern.

In this problem, the sounds are those of an S-type submarine.

PATTERN FOR RECORD XVI

The buoys are in a cross with Orange on top (north), Purple in the center, Yellow on left, Blue on right and Red below (south). The submarine is traveling south below the red buoy.

[13]


In Record XVII the conventional 5-buoy pattern is used again (see diagram). Submarine propeller beats are heard on Purple, Orange, and Blue frequencies on the first round of listening. The loudest signal is on the Orange frequency.

On the second round, propeller beats are heard on Purple, Orange, and Yellow frequencies. Obviously the sub is going in the direction of the Yellow buoy, but is still close to the Orange buoy.

The sub heard in this problem is an S-type boat.

PATTERN FOR RECORD XVII

The buoys are in a cross with Orange on top (north), Purple in the center, Yellow on left, Blue on right and Red below (south).
The sub is going in the direction of the Yellow buoy, but is close to the Orange buoy.

[14]


In Record XVIII, a 5-buoy pattern is used once more. On the first round of listening a surface craft is heard on the Blue frequency, a sub is heard on Yellow frequency. On the second round of listening the surface craft (a DE) is heard on Purple and Blue frequencies, and the sub signal is getting weaker on the Yellow frequency.

Both vessels are apparently going in a westerly direction, with the sub leaving the buoy pattern and the DE ("X" on the diagram) entering the buoy pattern.

PATTERN FOR RECORD XVIII

A sub is heard on Yellow frequency. On the second round a DE is heard on Purple and Blue and the sub is getting weaker on the Yellow. Both vessels are going in a westerly direction, the sub leaving the pattern and the DE entering.

[15]


More stickfigure women with record heads.  The are singing 'Papas' off to the seven seas.  Sky Anchors Away

THE TEXT OF THE RECORDS

Following are the actual scripts for the training records. These scripts may be studied to good advantage in the preparation of your teaching program.

[16]


I. Introduction to Submarine Sounds

To use the Expendable Radio Sono-Buoy effectively, you must be able to detect the sounds produced•by a submarine. This isn't always easy, since modern submarines are designed to make very little noise. Furthermore, you must pick out the sub signals from the background noise which is heard over any underwater listening system.

This background noise is produced by water surging around the hydro- phone, by waves breaking on the surface, and by similar water disturbances. Water noise has no definite pitch or rhythm. Over the Expendable Radio-Sono Buoy, it sounds like this:


Sound: Water noise

The sounds made by surface craft and by submarines usually have either a marked rhythm or a distinct pitch. Therefore, these sounds stand out from the water noise.

The sounds from a submarine-and these are the sounds in which you are specially interested -may be caused by the propellers, by the main driving machinery, and, to a lesser degree, by operation of auxiliary equipment. Listen first to the sound of a submarine's propellers.


Sound: Submarine propeller beats

(Fade down in 10 seconds and:
"Note that these propeller sounds have a definite rhythm and can be easily counted.")


Now you'll hear the whine of the DRIVING MACHINERY.


Sound: Submarine machinery sounds
The operation of auxiliary equipment aboard a sub produces certain characteristic sounds. In the next example, you will hear the intermittent sounds produced by power operation of the bow and stern planes.

[17]


Sound: Submarine auxiliary motor sounds
Often, you will hear machinery sounds and propeller beats together as in the following example.
Sound: Submarine machinery whine and propeller beats On this record you have heard underwater sounds picked up by the Expendable Radio Sono-Buoy. In the records which FOLLOW, you will hear more detailed examples of sounds from submarines, surface craft, and miscellaneous sources.

II. Cavitation: Effect of Depth and Speed (Fleet Type Submarine)


Sound: Periscope depth, 7 knots (propeller beats)
These sounds are from a submarine's propellers. As the propellers turn rapidly they create small, momentary cavities in the water. This effect is called CAVITATION. When the water rushes back into the cavities, it produces the . sounds recognized as PROPELLER BEATS.
Sound: Periscope depth, 7 knots (propeller beats)
CAVITATION depends mainly upon the speed and depth of the submarine. For example, an American fleet type submarine running at periscope depth produces cavitation at speeds of 3 1/2 to 4 knots and above. When its speeds falls below 3 1/2 knots, cavitation is usually absent, and you hear only machinery sounds. . . . Here is a sub of this type at a speed of 3 knots, periscope depth.

[18]


Sound: Periscope depth, 3 knots (machinery sounds)
Now the submarine speeds up to 6 knots. It is still at periscope depth.
Sound: Periscope depth, 6 knots (propeller beats)

(Fade down in 10 seconds and:
"At this speed, cavitation is present and you can easily hear the beat of the propellers.")


Cavitation ALSO depends on the depth of the submarine. As the depth becomes greater cavitation decreases.

In the previous example, a sub at 6 knots and periscope depth gave distinct propeller beats. In the next example you will hear the same sub at the same speed, but at 250 feet. At this depth, a speed of 6 knots is too slow to produce cavitation. Consequently, you hear no propeller beats.


Sound: 250 ft. depth, 6 knots (machinery sounds)
If the sub stays at 250 feet, but speeds up, cavitation will begin at about 61/2 knots. At 8 knots, the propeller beats will be clearly audible.
Sound: 250 ft. depth, 8 knots (propeller beats)

(Fade down in 5 seconds and:
"Depth: 250 feet. Speed: 8 knots.")


From this record you have learned the following facts about cavitation:

First, cavitation occurs when a sub's propellers turn rapidly in the water. Small momentary cavities are created, and the surrounding water rushes into these cavities, resulting in the sounds recognized as propeller beats.

Second, the main factors affecting cavitation are the submarine's speed and depth. For example, an American fleet type sub, at periscope depth, produces cavitation at speeds of 3 1/2 to 4 knots and above. The same type sub, at a depth of 250 feet, produces cavitation at 6 1/2 knots and above.


[19]


III. Cavitation: Effect of Depth and Speed (Old Type Submarine)

Cavitation effect does not occur at the same speeds for all submarines. Some submarines produce cavitation at a slower speed than others. When listening to our small older type sub you will usually hear propeller beats, unless the sub is running at almost minimum speed.

In the following example, you will hear an American S-boat (built about 1920) running at periscope depth. Range: 500 yards. Speed: 3 knots.


Sound: Periscope depth, 3 knots (propeller beats)

(Fade down in 10 seconds and:
"In this example, the swish of the propellers is quite evident.")


At a depth of 100 feet, and a speed of 3 knots, the sub sounds like this. Notice the hum of the machinery in the background.
Sounds: 100 ft. depth, 3 knots (propeller beats)
The same sub, periscope depth. Range: 500 yards. Speed: 2 1/2 knots.
Sound: Periscope depth, 2 1/2 knots (propeller beats)

(Fade down in 10 seconds and:
"The sub is now going too slow to produce distinct cavitation sounds. The propeller beats are weak and irregular.")


And now, at a speed of 2 1/2 knots but at a depth of 100 feet.
Sound: 100 ft. depth, 2 1/2 knots (machinery sounds)

(Fade down in 10 seconds and:
"At this depth and speed, you hear only a faint machinery whine. There are no cavitation sounds.")


[20]


As illustrated by these examples, this type sub produces cavitation at slower speeds than the modern fleet type which was described on Record 2. The smaller, older boat produces cavitation at speeds of 2 1/2 knots and above at periscope depth. At a depth of 100 feet, the sub produces cavitation at speeds of 3 knots and above.
IV. Estimation of Submarine's Speed by Counting RPM

A submarine's propeller beats usually correspond to the turns of the propeller shaft: there is one beat for each turn of the shaft. By counting the beats in one minute, you can learn the RPM of the sub and have some indication of its speed.

For instance, American fleet type submarines make about 20 RPM per knot when submerged. Our smaller older type subs make about 40 to 50 RPM per knot. If you were listening to the propeller beats from a fleet type sub and counted 100 beats in one minute, you would know the sub was making a speed of about 5 knots. The smaller. sub at the same RPM of 100, would be making a speed of 2 or 3 knots.

In the following example, assume that you are listening to a fleet type submarine. At the word "Start", begin counting the beats. At the word "Stop", end your count. The time between Start and Stop will be 15 seconds. Are you ready?


Sound: Fleet type submarine-120 RPM-6 knots
(Interrupt in 2 seconds with: "START")
(Interrupt in 17 seconds with: "STOP")
That count was for 15 seconds, or one-quarter of a minute. So, to get the RPM, or revolutions per minute, multiply your count by four.

(Pause 2 seconds)

The correct count for 15 seconds was 30. Multiplying this count by 4 gives 120, the correct RPM of the sub in this example.

Since you were listening to a fleet type submarine, which makes 20 RPM per knot, the speed of the sub is 120 divided by 20, or 6 knots. In the following examples, count the propeller beats for 15 seconds, by a watch or clock. Then multiply your count by 4 to get the correct RPM. Each example will last about 20 seconds, but no start or stop signal will be given. Ready: here is the first example.


[21]


Sound: Old type submarine- 150 RPM -3 knots
The correct RPM for the example was 150. The sub was a small type which makes about 50 RPM per knot. 150 divided by 50 gives an approximate speed of 3 knots.

Now, get ready for the next example. Take a count for 15 seconds. Then multiply your count by 4 to get the correct RPM.


Sound: Fleet type submarine - 140 RPM- 7 knots
That was a fleet type sub. It makes about 20 RPM per knot. Figure out the sub's speed.

(Pause 3 seconds)

The RPM was 140. The sub's speed as approximately 7 knots.

If you can determine the speed of sub heard over the buoy equipment, it may help you in tracking that sub.

Remember, to determine the speed of a submarine, count its prop beats and find the number of revolutions in 1 minute. This figure divided by the RPM per knot will give the sub's approximate speed.

Our modern fleet type subs make about 20 RPM per knot; our older smaller type subs make about 40 to 50 RPM per knot. Small German subs, according to limited available information, make about 40 RPM per knot. For further information on enemy submarines consult the latest official reports.


V. Effect of Underwater Range on Submarine Sounds

The range at which a submarine can be detected by an Expendable Buoy depends on two factors: the amount of noise the submarine makes, and water conditions.

Some submarines are naturally noisier than others and every submarine makes more noise as it increases speed. Everything else being equal, a noisy sub can be detected at a greater distance than a quiet one.

[22]


Because of these variable factors, no definite range of detection can be given. With a quiet sub at slow speed, and poor water conditions, the sound range may be limited to a few hundred yards. Under good conditions, the Expendable Buoy will detect a submarine at a range of several thousand yards.

The distance of the submarine from the Expendable Buoy will affect the strength of the sounds heard. When the sub is close to the Buoy, the sounds will be strong. As the sub moves farther away, the signals become weaker, until finally they are completely lost in the background water noise.

In the following examples, you will hear a submarine at close range, then at long range. In both cases the submarine is at periscope depth, and at a speed of 6 knots.

First, the sub at a range of approximately 200 yards.


Sound: Range -200 yards
And now, at a range of 1,000 yards. Although the propeller beats are weaker, you can still hear them through the water noise if you listen closely.
Sound: Range-1,000 yards
Let's listen once again to the sub at 200 yards.
Sound: Range - 200 yards
This difference in volume is useful when you are trying to locate a sub- marine. For instance, suppose you are listening over two buoys of a pattern. You tune in on one - and you hear -
Sound: Range - 1,000 yards
Then you tune to the other ----

[23]


Sound: Range - 300 yards
The sounds from the first buoy were weak. The sounds from the second buoy were strong. Evidently, the sub is closer to the second buoy than it is to the first.

Comparative listening is used in this manner with all the buoys of a pattern, so that you may determine the approximate location of the submarine.


VI. Comparison Between Sounds Produced by Surfaced and Submerged Submarine

You should be able to distinguish the sounds of a submarine on the surface from the sounds of a submarine which is submerged. In a "gambit", or baiting', maneuver, your plane will fly out of the area and wait for the sub to come up. Then you must be able to tell, by listening, when the sub is on the surface. There is usually a change in the character of the signal received. You may still continue to hear propeller beats but you may also begin to hear the roar of the diesel engines.

In the following examples, the sounds from a submerged submarine will be compared with the sounds from a surfaced submarine.

First, a sub at periscope depth. Speed: 3 knots. Range: 500 yards.


Sound: Periscope depth, 3 knots
And now, the same sub on the surface. Speed: approximately 7 knots. Range: 800 yards.
Sound: On surface, 7 knots Once again, submerged

[24]


Sound: Periscope depth, 3 knots
In the next example you will hear a sub first at periscope depth. Speed: 4 knots. Range: 300 yards. In the course of the example, the sub blows its tanks, surfaces, and proceeds away from the buoy at a speed of 7 knots.
Sound: Blowing tanks and surfacing (Fade down in 40 seconds and:
"The sub is now on the surface and is preparing to change over to Diesels.")
(Fade down in 1:05 minutes and:
"The sub is now on Diesels and proceeding away from the buoy. Range: 500 yards.")
The success of the gambit or baiting maneuver depends upon your ability to interpret the sounds you hear over the Expendable Buoy. Your buoy may not be close enough to the sub to pick' up sounds such as the blowing of tanks, but you should be able to distinguish the sounds of a sub's Diesels from it's electric motors.

VII. Interfering Sounds: Submarine and Destroyer Escort

In joint air-surface action, perfection in teamwork is required:

Aircraft will keep surface craft notified of any indications of the submarine's position.

Aircraft will guide surface craft to the position by use of radio, blinker, surface markers, or zooming the spot.

Aircraft should stand ready to attack the submarine if brought to the surface by surface craft attack.

When the Expendable Buoy is used during joint air-surface action, it will be necessary for you to distinguish between the sounds of the submarine and the surface craft.

In the following examples you will hear the sounds from a submarine and a destroyer escort.

First, the submarine alone. Speed: 3 knots. Range: 500 yards.


[25]


Sound: Submarine, periscope depth, 3 knots
Next, destroyer escort. Speed: 15 knots. Range: 2,000 yards.
Sound: DE, 15 knots
And now, both the sub and the DE. In the first part of the example, the sub is lying-to at periscope depth 500 yards from the buoy. The DE is at a distance of 1,500 yards. During the example the sub starts its motors and speeds up to 5 knots. The submarine sounds are so loud that they mask the DE sounds.
Sound: Submarine, 500 yards; and DE, 1,500 yards
Assume that you have picked up a submarine over a buoy. You have narrowed down the area of search and have reported the sub's approximate location to a destroyer escort which is now approaching the area.

At first the signal from the sub will be stronger than that of the DE.


Sound: Submarine, periscope depth, 5 knots; DE,10 knots approaching from 1,000 yards

(Fade down in 10 seconds and:
"The sub is 600 yards from the buoy. Speed: 5 knots. The DE is 1,000 yards away and its signal is drowned out by the sub. As the DE comes closer, at a speed of 10 knots, its signal gradually becomes audible, until it predominates over the sub's.

"Listen for the fast prop beat of the sub and the slow prop beat of the DE.")

(Fade up sound)
(Fade down in 40 seconds and:
"Range of DE: 600 yards. Sub the same.")


If the surface craft fails to establish contact with the submarine or loses contact during an attack, it may withdraw from the area and direct the aircraft to resume searching and tracking procedures.

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VIII. Sounds Produced by Activities Aboard Submarine

The most important sounds made by a submarine are produced by its propellers and machinery. However, you can sometimes hear other, weaker sounds such as the whine of motor generators, the slamming of hatches, and so on. Usually the submarine must be within 100 yards of the Expendable Buoy before these secondary sounds can be picked up.

In the following examples, you will hear some miscellaneous submarine sounds.

First, the operation of a trim pump.


Sound: Operating trim pump and bleeding down ballast tank (Interrupt in 13 seconds with: "Bleeding down a ballast tank.")
The radar-training motor-generator.
Sound: Operating radar-training motor-generator
Members of the crew pounding on pipes and on bulkheads.
Sound: Pounding on pipes and bulkheads
Torpedo Data Computer.
Sound: Operating Torpedo Data Computer
Members of the crew slamming bulkhead doors.
Sound: Slamming bulkhead doors
Announcement over the public address system, and shouts from the crew.

[27]


Sound: Announcing over P.A. system, shouting of crew
In the next example you will hear a series of alarms, and another announcement over the public address system.
Sound: Sounding alarms
The final example is the sound of a submarine charging its batteries. This is a surface operation, and as a general rule, it is carried on at night.
Sound: Charging batteries

IX. Marine Life Sounds

In your work with the Expendable Radio Sono-Buoy, you will probably hear many sounds other than submarine sounds. Surface craft, torpedoes, and depth charges all give characteristic signals, and, strangely enough, certain fish and marine animals also produce peculiar noises.

This record will give some examples of the marine life sounds you may hear over the Expendable Buoy.

First, the fish known as the "croaker." This fish grows to a length of one or two feet and is generally found along the Atlantic and Gulf coasts. it produces a staccato sound like a riveting gun.


Sound:. Croakers
Next, the black drumfish. This fish is usually three or four feet long, and, like the croaker, is found along the Atlantic and Gulf coasts. As its name implies, the drumfish makes ,a hollow, thumping noise like a drum.
Sound: Black drumfish.

[28]


In the next example you will hear the snapping shrimp. The shrimp is found in large numbers in shallow southern waters, both in the Atlantic and Pacific. It produces a harsh clicking noise.
Sound: Snapping shrimp
The Garibaldi fish grows about one foot in length. It is found in the waters off the coast of California. This species produces harsh clicking noises, probably with its teeth.
Sound: Garibaldi
In the final example, you will hear a school of porpoises. The common porpoise grows to a length of 5 to 8 feet and is found in both the Atlantic and Pacific.
Sound: Porpoises
In this record, you have heard just a few examples of marine life. Actually, there are many more species that produce sounds.

You may hear underwater sounds that you are unable to identify. If they are irregular and occur intermittently, they are probably natural sounds such as those you have just heard. If the sounds are regular in rhythm or continuous, they are probably man-made, and caused by a submarine or surface craft.


X. Surface Craft Sounds

Surface ships, as well as submarines, produce underwater sounds. These sounds may come from the ship's propellers, its machinery, or its auxiliary gear. In most cases, you will be able to sight any surface craft in your area, but there may be times when you cannot see a ship but you can hear one. Then you will want to know what it is.

In the following examples, you will hear sounds from a surf landing boat, a cruiser, a destroyer, a battleship, a freighter, and a destroyer escort.

First, a surf landing boat.


[29]


Sound: Surf Landing Boat - 15 knots
Next, the cruiser, USS SAN JUAN.
Sound: Cruiser - 9 knots
The destroyer, USS NICHOLSON.
Sound: Destroyer - 14 knots
The battleship SOUTH DAKOTA.
Sound: Battleship - 7 knots
The freighter BETHORE.
Sound: Freighter - 8 knots
In the final example, you will hear the Destroyer Escort, Number 794 as recorded over the buoy equipment. The DE is going away from the buoy at a range of about 2,000 yards.
Sound: Destroyer Escort - 15 knots

XI. Torpedo, Minesweeper, and Foxer Sounds

On this record are sound examples from an electric torpedo, an air driven torpedo, a mine sweeper, and a Foxer.

First, a German electric torpedo. It has a whining sound, with a rapid staccato beat from its propellers.

[30]


Sound: German electric torpedo
Next, a German air-driven torpedo. It has a low roaring sound, and again, a rapid propeller beat.
Sound: German air torpedo
An acoustic mine sweeper. This is usually a strong stuttering signal, which may be picked up at ranges as high as 20 miles.
Sound: Acoustic minesweeper
In the final example, you will hear the sound of a Foxer. A Foxer is a noise generator trailed behind a ship as a protection against acoustic torpedoes. It has a loud, buzzing signal.
Sound: Foxer
XII. Depth Charge Explosions

Underwater explosions heard over an Expendable Buoy may not sound quite as you would expect. There is no sharp report as heard in the air, but a noise which can be described as a roaring sound of great intensity that lasts for many seconds.

The explosions you will hear in the following examples were made with Mark 47 Depth Charges, set to explode at a depth of 25 feet.

In the first example, the depth charge is dropped 2 miles from the buoy.


Sound: Range - 2 miles

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Next, a depth charge dropped 1 mile from the buoy.
Sound: Range - 1 mile
Depth charge dropped 1,000 yards from the buoy.
Sound: Range - 1,000 yards
And now, a depth charge dropped only 100 yards from the buoy.
Sound: Range - 100 yards
You perhaps noticed that the -intensity or loudness of the depth charge examples was about the same regardless of the range. This effect was caused by overloading. The explosions were all so extremely loud that the buoy receiver was overloaded and produced only its maximum signal.

The final example will give you an idea how your depth charges sound to the enemy. The sounds were recorded inside a submarine as depth charges were dropped 300 yards away.


Sound: Depth charges as heard aboard submarine

XIII. Identification Test

The following examples will give you an opportunity to check your ability to recognize underwater sounds. At the end of each example, write down the sound or sounds that you hear. Be as specific as possible. That is, if you think you hear the propeller beats of a submarine, write "Prop beats of sub." If you hear the machinery sounds also, write "Prop beats and machinery sounds of sub" - and so on.

Are you ready?

No. 1


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Sound: Water noise
No. 2
Sound: Submarine propeller beats
No. 3
Sound: Submarine machinery sounds
No. 4
Sound: Water noise
No. 5
Sound: Submarine's auxiliary motors (bow and stern planes) No. 6
Sound: Minesweeper
No. 7
Sound: Submarine propellers and machinery No. 8

[33]


Sound: Croakers
No. 9
Sound: Submarine charging batteries
No. 10
Sound: Submarine propeller beats and depth charge
End of test

XIV. Identification and Turncount Test

After each of the following examples, write down the sound or sounds which you hear. Some of the examples will be comparatively simple, while others will be more complex.

No. 1


Sound: Submarine propeller beats
No. 2 Sound: Water noise
No. 3

[34]


Sound: Submarine propeller beats and minesweeper
No. 4
Sound: Sub on surface No. 5
Sound: DE
No. 6
Sound: Water noise and depth charge In the final example, No. 7, you will hear the propeller beats of an American fleet type submarine. This sub makes about 20 RPM per knot. Count the RPM and figure the sub's SPEED IN KNOTS. Write down the RPM and speed of the sub.
Sound: Propeller beats, 120 RPM - 6 knots End of test

XV. Search Problem

Suppose that a submarine has been reported in a certain area. Your plane is sent out to investigate. You drop a pattern of three buoys. Lay out the pattern on your paper. Purple in the center, Orange at North, and Blue at East. (Pause)

[35]


In actual practice, you would listen to each buoy after launching it. Hearing a submarine signal on any particular buoy might make it necessary to change your pattern. However, for purposes of this test, assume that you drop all three buoys and then begin listening.

First you tune to Purple.


Sound: Weak prop beats
You tune to Orange
Sound: Water noise
You tune to Blue
Sound: Strong prop beats You turn back to Purple.
Sound: Weak prop beats Orange
Sound: Water noise
Blue
Sound: Strong prop beats

[36]


Study your buoy diagram. Indicate the location of the submarine with the letter S.

Let's review the problem. On Purple frequency, you heard weak propeller sounds. On Blue, you heard strong propeller sounds. On the Orange buoy, you heard only water noise. Therefore, the 'submarine is probably quite a distance from Orange and between Purple and Blue. Since the signal came in strong over Blue, the sub is probably quite close to the Blue buoy.

Similar problems will be given on following records. As you hear the signal from each frequency, write down on your pattern whether the signal is strong or weak. This will assist you in locating the submarine.


XVI. Search Problem

This time, assume that you have dropped a pattern of five buoys and you are now ready to tune from one buoy to another. Draw a pattern on your paper. Purple in the center, Orange at North, Blue at East, Red at South, and Yellow at West. As you listen to each frequency, write down on your pattern the signal heard and the relative strength of the signal.

You tune to Purple.


Sound: Weak propeller beats And next, to Orange
Sound: Water noise Blue
Sound: Water noise

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Red
Sound: Strong propeller beats
Yellow
Sound: Weak propeller beats
You again tune to Purple.
Sound: Water noise Orange
Sound: Water noise Blue
Sound: Water noise Red
Sound: Strong propeller beats
Yellow

[38]


Sound: Water noise
Mark the sub's location with the letter S. If any other craft was heard in the area, mark its location with the letter X. Comment, briefly on the sounds you heard. Show where more buoys might be dropped to good advantage.

XVII. Search Problem

In this problem, assume that you have dropped a pattern of five buoys. Draw the pattern on your paper. Purple in the center, Orange at North, Blue at East, Red at South, and Yellow at West.

As you listen to each frequency, write on your pattern the signal heard and the relative strength of the signal.

You tune to Purple.


Sound: Medium propeller beats And next, to Orange
Sound: Strong propeller beats Blue
Sound: Weak propeller beats
Red Sound: Water noise

[39]


Yellow
Sound: Water noise
You turn back to Purple.
Sound: Weak propeller beats Orange
Sound: Very strong propeller beats Blue
Sound: Water noise Red
Sound: Water noise Yellow
Sound: Weak propeller beats
Mark the sub's location with the letter S. If any other craft was heard in the area, mark its location with the letter X. Comment briefly on the sounds heard. In what direction is the sub travelling? Show where more buoys might be dropped to good advantage.

[40]


XVIII. Search Problem

Assume that you have dropped a pattern of five buoys. Draw the pattern on your paper. Purple in the center, Orange at North, Blue at East, Red at South, and Yellow at West.

As you listen to each frequency, write on your pattern the signal heard and the relative strength of the signal.

You tune to Purple.


Sound: Water noise Orange
Sound: Water noise Blue
Sound: Weak DE sounds Red
Sound: Water noise Yellow
Sound: Medium submarine propeller beats And now you turn back to Purple

[41]


Sound: Weak DE sounds
Orange
Sound: Water noise
Blue
Sound: Medium DE sounds Red
Sound: Water noise
Yellow
Sound: Weak submarine propeller beats Mark the sub's location with the letter S. If any other craft was heard in the area, mark its location with the letter X. Comment briefly on the sounds heard. In what direction is the sub travelling? Show where more buoys might be dropped to good advantage.

[42]


ADDITIONAL RECORDS

RECORDS XIX, XX - Enemy Submarine Sounds

After this manual had been prepared, two new records were added to the Expendable Radio Sono-Buoy Training Records Album. They are the records of the sounds heard during actual anti-submarine operations. The sounds included are: enemy submarine propeller beats, explosions, and other sounds heard during the course of operations.

 

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