Operational Characteristics of U.S. Naval Mines (U), ORD 696(B), 1959, shows the basics of underwater offensive mines.

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Richard Pekelney


ORD 696(B)
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ORD 696(B)


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1. ORD 696(B), OPERATIONAL CHARACTERISTICS OF U.S. NAVAL MINES (U), is a Confidential Registered RPS-distributed publication. It shall be transported, stowed, safeguarded and accounted for in accordance with the instructions contained in the effective edition of the Registered Publication Manual.

2. ORD 696(B) is effective upon receipt, superseding ORD 696(A) dated 18 October 1954 which should be destroyed in accordance with instructions contained in the effective edition of the Registered Publication Manual when authorized by RPS 36.

3. This publication summarizes basic information about U.S. Naval Mines for the purpose of enabling technically trained personnel to select the most suitable mines for a specific situation. When additional verified material is available, or new mines are released, this publication will be revised to include the information. Reports concerning errors in this publication or additional substantiated information should be forwarded to the Chief of the Bureau of Ordnance, Department of the Navy, Washington 25, D. C., Attention: Code (ReU6).



6. This publication shall not be carried in aircraft for use therein.

Rear Admiral, U.S. Navy
Deputy Chief, Bureau of Ordnance
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Letter of Promulgation to ORD 696(B) III (REVERSE BLANK) ORIGINAL
List of Effective Pages V, VI ORIGINAL
Table of Contents VII, VIII ORIGINAL
Record of Corrections IX, X ORIGINAL
Considerations in Selecting Mines for Tactical Use 1 through 10 ORIGINAL
Mine Mk 6 Mod 0 11 through 14 ORIGINAL
Mine Mk 6 Mod 4 15 through 18 ORIGINAL
Mine Mk 6 Mod 7 19 through 22 ORIGINAL
Mine Mk 6 Mod 8 23 through 26 ORIGINAL
Mine Mk 6 Mod 10 27 through 30 ORIGINAL
Mine Mk 6 Mod 11 31 through 34 ORIGINAL
Mine Mk 6 Mod 14 35 through 38 ORIGINAL
Mine Mk 10 Mod 3 39 through 42 ORIGINAL
Mine Mk 10 Mod 7 43 through 46 ORIGINAL
Mine Mk 10 Mod 9 47 through 50 ORIGINAL
Mine Mk 16 Mod 1 51 through 54 ORIGINAL
Mine Mk 18 Mod 0 55 through 58 ORIGINAL
Mine Mk 25 Mod 0 59 through 62 ORIGINAL
Mine Mk 25 Mod 1 63 through 66 ORIGINAL
Mine Mk 25 Mod 2 67 through 70 ORIGINAL
Mine Mk 27 Mod 2 71 through 74 ORIGINAL
Mine Mk 27 Mod 3 75 through 78 ORIGINAL
Mine Mk 27 Mod 4 79 through 82 ORIGINAL
Mine Mk 27 Mod 5 83 through 86 ORIGINAL
Mine Mk 36 Mod 1 87 through 90 ORIGINAL
Mine Mk 36 Mod 2 91 through 94 ORIGINAL
Mine Mk 36 Mod 3 95 through 98 ORIGINAL
Mine Mk 39 Mod 0 99 through 102 ORIGINAL
Mine Mk 49 Mod 0 103 through 106 ORIGINAL
Mine Mk 49 Mod 1 107 through 110 ORIGINAL
Mine Mk 49 Mod 2 111 through 114 ORIGINAL
Mine Mk 50 Mod 0 115 through 117 (REVERSE BLANK) ORIGINAL
Mine Mk 51 Mod 0 119 through 122 ORIGINAL
Mine Mk 51 Mod 1 123 through 126 ORIGINAL
Mine Mk 52 Mod 0 127 through 130 ORIGINAL
Mine Mk 52 Mod 1 131 through 134 ORIGINAL
Mine Mk 52 Mod 2 135 through 138 ORIGINAL
Mine Mk 52 Mod 3 139 through 142 ORIGINAL
Mine Mk 52 Mod 4 143 through 146 ORIGINAL
Mine Mk 52 Mod 5 147 through 150 ORIGINAL
Mine Mk 52 Mod 6 151 through 154 ORIGINAL
Mine Mk 53 Mod 0 155 through 158 ORIGINAL
Controlled Mine System Mk 1 Mod 0 159 through 166 ORIGINAL



Controlled Mine System Mk 2 Mod 0 167 through 173(REVERSE BLANK) ORIGINAL
Appendix C C-1 through C-7 (REVERSE BLANK) ORIGINAL
Appendix D D-1 through D-3 (REVERSE BLANK) ORIGINAL
Appendix E E-1 through E-3 (REVERSE BLANK) ORIGINAL
Appendix F F-1 through F-3 (REVERSE BLANK) ORIGINAL
Appendix G G-1 through G-12 ORIGINAL



Considerations in Selecting Mines for Tactical Use 1
Mine Mk 6 Mod 0 11
Mine Mk 6 Mod 4 15
Mine Mk 6 Mod 7 19
Mine Mk 6 Mod 8 23
Mine Mk 6 Mod 10 27
Mine Mk 6 Mod 11 31
Mine Mk 6 Mod 14 35
Mine Mk 10 Mod 3 39
Mine Mk 10 Mod 7 43
Mine Mk 10 Mod 9 47
Mine Mk 16 Mod 1 51
Mine Mk 18 Mod 0 55
Mine Mk 25 Mod 0 59
Mine Mk 25 Mod 1 63
Mine Mk 25 Mod 2 67
Mine Mk 27 Mod 2 71
Mine Mk 27 Mod 3 75
Mine Mk 27 Mod 4 79
Mine Mk 27 Mod 5 83
Mine Mk 36 Mod 1 87
Mine Mk 36 Mod 2 91
Mine Mk 36 Mod 3 95
Mine Mk 39 Mod 0 99
Mine Mk 49 Mod 0 103
Mine Mk 49 Mod 1 107
Mine Mk 49 Mod 2 111



Mine Mk 50 Mod 0 115
Mine Mk 51 Mod 0 119
Mine Mk 51 Mod 1 123
Mine Mk 52 Mod 0 127
Mine Mk 52 Mod 1 131
Mine Mk 52 Mod 2 135
Mine Mk 52 Mod 3 139
Mine Mk 52 Mod 4 143
Mine Mk 52 Mod 5 147
Mine Mk 52 Mod 6 151
Mine Mk 53 Mod 0 155
Controlled Mine System Mk 1 Mod 0 159
Controlled Mine System Mk 2 Mod 0 167
Appendix A - Mine Carrying Capacities of Aircraft A-1
Appendix B - Mine Carrying Capacities of Surface Vessels and Submarines B-1
Appendix C - Damage Range Curves for Cargo Vessels and U. S. Naval Vessels C-1
Appendix D - Operating Times of Sterilizers D-1
Appendix E - Clock Starter Delays for Mines Exposed to Cold Temperatures E-1
Appendix F - Launching Speeds and Altitudes of Aircraft Planted Mines F-1
Appendix G - Percentage Actuation Depth Curves G-1


Record of Corrections


Record of Corrections

This pamphlet presents a summary of certain operational characteristics for U. S. Naval mines. It is intended for use by personnel with sufficient technical background and training in mine field planning to select the characteristics most vital in a particular application. The arrangement of the book has been planned to expedite the identification of the mine having the most suitable group of characteristics. The data presented is intended only for rough comparisons and preliminary estimates of the suitability of the particular mine.

Maximum limits for expected uses are given. However, special conditions which are beyond the scope of this publication may limit the uses of any mines. Additional data on operation, assembly, testing, handling, and planting in connection with a particular tactical problem may be found in the pamphlets on the various mines. These publications are included under "References" following the data for each mine.

The data for each mine appear on succeeding sheets. The sections, or groups of mine data sheets, are arranged numerically by Mine Mark and Mod numbers, with the sections for Controlled Mine Systems Mk 1 Mod 0 and Mk 2 Mod 0 immediately following that for Mine Mk 53 Mod 0. The characteristics are presented in as nearly the same order as possible to facilitate comparison. For the same reason, headings and nomenclature have been made as nearly uniform as feasible.

Below the main title of each section is a photograph of the mine, showing the distinguishing external features, followed by a tactical notation under the heading of DESCRIPTION. Characteristics and other data are classified under common headings as listed below with a summary of the facts included under each heading. A glossary of terms used to describe mine characteristics is included at the end of this section.


The primary tactical features of the mine are stated. Important miscellaneous facts may also be given here.


The following three factors serve to classify each mine.

  Planted Position: The positions are bottom or moored.

Launching Means: Aircraft, submarine, or surface vessel as used to convey and place the mine in the proper planted location.

Firing Method: Contact or influence as used to detect a ship. For contact mines, the means used to initiate detonation is given. For influence mines, the type of influence employed is given.


Explosive weights are stated within limits of ±5% for the currently preferred explosive at the time of publication. This accuracy is sufficient for the purposes of this book. Greater accuracy in explosive loading is possible, but experience indicates that unforeseen variables may cause variations within this stated tolerance.

Many mine cases are now loaded with other than the currently preferred explosive, which is the only explosive mentioned under "Explosive Charge."

Information necessary to evaluate the damage to submarines or cargo vessels is grouped together in Appendix C. The damage data are shown for the approved type of explosive for each mine. Reference data are supplied to enable trained personnel to convert information to alternate explosives.


The assembled weight of each service assembly is given to an accuracy of ±5%. Variations within this limit include differences in the mine case, component, explosive, and in the type of parts selected for assembly.


The subject of buoyancy has been considered of sufficient importance to be shown on the first page of each group of mine sheets. It is obvious that the total buoyancy of a mine assembly must be negative to insure sinking. In the case of a moored mine, the mine case has a positive buoyancy that would cause it to float, but the greater negative buoyancy of the anchor gives the mine assembly a total buoyancy


that is negative. For moored mines, buoyancies of cases and anchors are given in addition to total buoyancy,as an aid in evaluating stability. Data for Mine Mk 6 Mods 4, 7, 8, 10, 11, and 14 were corrected for the prime differences in the assemblies. Data for other mines were obtained by actual measurements or by assuming a cylindrical shape and making corrections for conical and rounded ends The accuracy of the negative buoyancy data is approximately ±5%.


The second page of each section includes a dimensional sketch showing the over-all form of the mine. Dimensions are shown for suspension lugs on aircraft mines or for track widths when mines are laid by surface vessels. Most dimensions are given to the nearest 1/8 inch. In some cases where 1/8 inch does not properly distinguish between assemblies of a mine, dimensions are given to the nearest 1/16 inch.


Mine-Carrying Capacity of Aircraft is grouped together to facilitate comparison and because the data are too numerous to fit on each mine sheet. The capacities given are maximum quantities based on physical limitations. In planning an operation the range, auxiliary equipment, and such items as armament required for the operation must be considered. Some data are estimates which have not been proved by trial and are noted as approximations. (See Appendix A.)

Mine-Carrying Capacity of Surface Vessels is based on the maximum physical limitations such as track space but also includes disassembled mines where such space is available. Normally other factors do not seriously decrease the carrying capacity of surface vessels. (See Appendix B.)

Mine-Carrying Capacity of Submarines is grouped together because the data are too numerous to fit on each mine sheet. The capacities given are maximum quantities based on the assumption that all the useable storage space is used to carry mines. Since it is often necessary to carry torpedoes as well as mines, the number of mines carried will usually be less than the figures given. An estimate of the mine carrying capacity for a given situation can be made by subtracting two Mk 10 or Mk 49

  mines or one Mk 27 mine for each torpedo carried. Range auxiliary equipment, and other operational requirements may also affect the total carrying capacity. Some data are estimates which have not been proved by trial and are noted as approximations. (See Appendix B.)

Launching Speeds and Altitudes of aircraft planted mines are governed by possible impact damage to the mines. Most aircraft mines are prepared in assemblies utilizing parachutes, and a further governing factor is the character of the particular parachute and release mechanism employed. A crucial consideration in the parachute is its strength as well as its ability to control the velocity of the falling mine. A limiting factor in some assemblies may be the ability of the parachute pack to withstand buffeting. In certain operational assemblies of several of the aircraft-planted mines, mine fairings are provided. One type of fairing reduces the drag characteristics of mines when externally mounted on aircraft and lessens buffeting tendencies. Such fairings consist of a nose and a tail section, the latter being released by static line and the force of the slip-stream when launched, the nose section breaking away when the mine strikes the water. The other type of fairing improves trajectory characteristics. It is employed with delayed opening parachute packs and breaks away when the mine strikes the water. Speed and altitude limits for mine laying by aircraft are the same for charges of TNT and HBX. (See Appendix F.)

Launching Speeds and Depths of submarines when planting mines are governed by possible impact between the mine and submarine when launching from bow tubes and by the maximum depth below which the mine will not function satisfactorily during planting. Limiting speeds when launching from bow tubes and depths below which mines should not be launched are given in the data sheets of each submarine-launched mine When launching from stern tubes, no speed limitations apply.


A statement of the difficulties encountered in sweeping is given under this heading. The difficulties may arise from the particular influence or combination of influences required, or from various operational settings which are provided in accordance with the doctrine set forth in NWIP 26-1.



Under this heading are listed the various settings which may be made to complicate sweeping, to provide target selection, to compensate for natural background phenomena, and to increase the flexibility of use of the mine. For each setting available on a given mine, the range available or the discrete settings which may be made are specified. The settings covered are listed below.

Arming Delay: Timing ranges are given, with any gaps in the range pointed out. Delay arming times given in this pamphlet will be extended by the amount of time required for soluble washers or arming cells to operate when these devices are used on the clock starter.

Sterilizing: Timing ranges are given for clock-type sterilizers, and the discrete steps are given for electrolytic sterilizers. The times given for sterilizing devices are nominal; that is, they are the times at which all of the mechanisms in a group may be expected to have operated. Many will operate considerably earlier.

Ship Counts: The minimum and maximum number of actuations which may be required for firing are given under this heading.

Firing Sensitivity: This item covers only the adjustments which may be made during mine assembly to vary the sensitivity of the mine to the influence field of the target. Adjustments which occur automatically with planting depth are covered under Operational Data, since it is this data which is affected by them.

Timing Periods: Where interlook dead period, time out period, live period, or intership dead period are adjustable, the information on available settings or range of settings is included for the particular period involved.


Under this general heading are data for determining the suitability of a particular mine for use under a given set of conditions. Included are items which may rule out the use of a certain mine (e. g. , planting depths), and items which may indicate that one mine is more suitable than another (e. g. , actuation data). In general, final choice of mine for a particular mission may be made only after a consideration of detailed data (from an operational characteristics pamphlet) in the terms of the doctrine and equations of NWIP 26-1.

  The data given herein are intended only for rough comparisons and preliminary estimates of the suitability of the particular mine.

Planting Depth: Under this item, maximum and minimum planting depths are given. For moored mines, limits of bottom depth and case depth are given. The maximum case depth is usually the depth beyond which water pressure will damage the mine case or mine components mounted in the case. When case depths near the maximum limit are planned, allowance must be made for case dip; magnitudes of expected dip are given under limitations. The maximum bottom depth is usually determined by the amount of cable available. Bottom depth figures for mines that adjust their mooring to variable depths are based on the assumption that the mine case is moored at the surface. This assures that any case depth within the limits given may be used at the maximum given bottom depth. Once the case depth is chosen, the maximum bottom depth may be increased by an amount equal to the planned case depth. Tables are used to present planting depth information that is not the same for all mine operational assemblies.

For bottom mines, planting depth, bottom depth, and case depth are the same since the mine lies on the bottom.

Minimum planting depth (case depth for moored mines) is determined either by the minimum hydrostatic pressure required to operate mechanisms or, for some aircraft-planted mines, by the possibility of mine damage upon impact with the bottom. Maximum planting depth for bottom mines is usually determined by the ability of the mine case and components to resist pressure damage.

Minimum Spacing: Minimum Spacing is defined herein as the least distance between planted mines at which explosion of one mine will neither render its neighboring mine inactive nor cause it to countermine. Lesser spacings might be used in some cases where the sacrifice of some neighboring mines could be permitted. This sacrifice should be based on possible damage but not on countermining, since countermining might eliminate the entire mine field. In making plans which require the sacrificing of some mines, operational pamphlets must be consulted.

Firing Mechanism: The preferred firing mechanism is identified for reference in determining the basis for the actuation data. Where alternates are approved in the General Requisites, that fact is noted. Minor variations


in actuation data may be found with alternate mechanisms; but for the intended uses of this publication, such differences may be neglected except where specifically noted.

Actuation Data and Damage Effectiveness: For contact-fired mines, actuation is assumed to be 100 percent, and only damage capabilities are presented under this item. For influence-fired mines, tables are provided which present data on the actuation and damage capabilities of the mine. These data are presented for various target classes and speeds and for various planting depths for each mine, and consist of listings of average firing widths for each condition. Where operational settings are available which affect firing width, only the maximum and minimum attainable for each condition are listed. The data presented are coded to provide approximate indications of the probability of achieving damage as a result of a mine actuation under the conditions involved. A dark background indicates good probability (0.75 or more) of achieving moderate damage; a light background indicates fair probability (between 0.5 and 0.75) of achieving moderate damage; and an underscore indicates poor probability (less than 0.5) of achieving moderate damage. Frequently, intermediate sensitivity settings will yield better damage probabilities than the maximum and minimum settings given in the tables. Mine operational characteristics manuals should be consulted for complete information.

The values of firing width given in the tables are rounded off to a degree consistent with the precision of the data from which they are derived. Where a zero appears in the table, a rounding-off from a slightly higher number has occurred, and a very slight probability of actuation still exists. On the other hand, a dash indicates that there is essentially no possibility of a firing occurring under the conditions given.

The damage coding for surface ships is based on data which applies to ships classified "strong" from the standpoint of damage resistance. Where the actual target is in the "weak" category, the coding is conservative at depths below 10 fathoms. Appendix C should be consulted to obtain a comparison of the damage capability against "strong" and "weak" ships from the standpoint of both athwartship distance and depth.

Depths given in these tables are measured from the surface of the water. For magnetic mines, data presented for surfaced submarines may be applied to the same submarines

  when submerged (except for mines having automatic sensitivity compensation for planting depth) by considering the depths as depths below the surfaced waterline of the submerged submarine. Damage codings for surfaced submarines are conservative when the actuation data are applied to submerged submarines, and no damage data for submerged submarines are presently available. The pressure and acoustic influences of submerged submarines are quite different from those of the same submarine when on the surface. Therefore, actuation data for mines using these influences cannot be directly applied to submerged submarines. Notes on the applicability of actuation data to submerged submarines are given below the tables in each mine section.

The data presented in these tables are extracts from and simplifications of the data presented in the various operational pamphlets. These pamphlets should always be consulted when detailed data are desired for planning a specific mining operation.


Current Effects: For moored mines Vertical Dip is given where information is available. The maximum expected dip is shown. Dip data are all theoretical and are based on uniform current over the full cable length. Except for more or less constant currents, such as the Gulf Stream, this condition does not exist. Many service tests indicate that water currents frequently vary in direction and velocity at different depths, and the dip would vary accordingly.

Walking data are not included. Present information indicates that "walking" occurs only on smooth hard bottoms such as rock or coral. This action is usually associated with combined current and wave action. Waves tend to lift the anchor and the current drags it slightly. Where the current is a tide, it is probable that the mine would be returned to its original position. On most bottoms, walking is not expected unless the current exceeds four knots.

For mines functioning on pressure or acoustic influence, the presence of appreciable components of current parallel to the target' s heading will affect the actuation characteristics of the mine. For pressure mines, the presence of current opposing movement of the ship results in a greater displacement of water (and a larger pressure signature) than would


result from a ship travelling at the same ground speed in still water. Likewise, current in the direction of travel results in a decreased pressure signature. For acoustic mines, current opposing motion results in a greater propulsion noise level than would result from a ship travelling at the same ground speed in still water. Likewise, current in the direction of travel results in decreased noise levels.

Bottom Effects: The nature of the bottom influences both Current Effects and Wave Effects. This item covers probable effects due to: soft bottoms (muddy); medium bottoms (sandy, soft clay, pebble, or hard packed silt which holds a mine or anchor but into which impact or water currents may cause the anchor or mine to penetrate slightly); and hard bottoms (into which the mine or anchor will never penetrate). Mines that are aircraft-laid in shallow water may be damaged on impact with hard bottoms. Mines laid on hard, sandy bottoms may tilt or rock as a result of water action on the sand. This may cause single magnetic looks, with resultant shortening of mine life but will not usually cause actuation.

Wave Effects: The motion of the mine case is influenced by Wave Effects as well as Bottom and Current Effects. Waves frequently cause water motion at depths of 30 feet and may cause disturbances to depths of 50 feet. These figures are rough approximations and do not apply to pressure effects which extend to greater depths.

The effect of waves on mines functioning on pressure influence may be severe. Present pressure - detecting devices will respond to certain waves as well as to ships. For multi-influence mines, the result may be merely elimination of the requirement for pressure influence as a condition of firing. In other cases, waves may cause excessive cycling and severe reduction in mine life.

Expected Life: It is often desirable to know how long a mine may be expected to be operable, ignoring sterilizer action. Usually, the most important variables in determining this figure are the condition of the battery when assembled and the water temperature in which the mine is planted. Other influences such as corrosion and roughness of water may be important. Further research may prove the importance of other factors. The Expected Life stated is an average under normal conditions. Notations concerning conditions which

  will materially shorten the normal life are given.

Maximum Life: This time is based on battery life and is intended as a safe figure, beyond which safe ship passage is assured. In compiling these figures, it has been assumed that sterilizers are not used or have become ineffective. Explosives do not deteriorate greatly and are always subject to detonation by severe impact or shock. Moored mines usually break away from their moorings long before batteries are dead and must be recognized as a hazard from impact or because extenders failed to retract.

Temperature: All service mines are suitable for use in normal waters of all climates. However, the "exposure" temperatures are important and apply to all circumstances before planting. High temperatures damage some devices directly and cause rapid deterioration in others.

In most cases low temperatures will not cause permanent injury to a mine. However, if a mine which has been exposed to very low temperatures for a long period of time is planted in acceptable water temperature, damage can occur. For example, one clock-delay mechanism widely used in mines must be allowed to warm up before it is started or it will not operate at all. Also, electrolytic sterilizer fluids may be frozen and delay sterilizer operation by the length of time required to thaw out the fluid.


Publications required to obtain additional data about particular mines are listed on the mine sheets. Publications which contain information about components of the subject mine are also listed.


It has been necessary to use codes, symbols, and abbreviations in order to present the data for each mine within four pages.

A series of dashes is used in spaces on charts and tables where no data apply. Spaces are left blank where data were not available at time of writing, so that the user of this publication may add such data as they become available.

In vertical dip charts, 0+ indicates a negligible



On actuation charts, the code indicating the probability of achieving moderate damage (good, fair, or poor) is given below the charts.

  It is assumed that abbreviations and symbols which are not explained in the text or in the footnotes will be readily understood; for example, "kt" for knots, "fm" for fathom, "oper. assy" for operational assembly, "M-Deg" for M-Degaussed.

This appendix is in tabular form and indicates the quantity of each mine assembly that designated aircraft can carry, differentiating between external and internal suspension of the mine. This appendix includes only those aircraft types for which carrying capacities were available at time of writing.


This appendix includes carrying capacities of specified minelaying craft and submarines.


These curves show damage patterns for designated cargo vessels, submarines, and U. S. Naval vessels expected from mine actuation at various distances. An explanation of the curves is included.


This appendix discusses CD-type and SD-type sterilizers, effect of delayed-arming on these sterilizers, and bleeder resistors . Tables of mechanism operating times are included where applicable


A description of the use of the nomograph is included, along with two typical problems to which it is applicable.


This appendix comprises a table showing limitations in speed and altitudes resulting from flight gear design or other characteristics for each aircraft planted mine assembly. Both bomb bay and external rack mountings are considered.


Curves for the mines included represent maximum depths for low percentage firing probabilities against specified classes of U. S. Naval Vessels, and are based upon maximum nominal sensitivities obtaining in each mine. The meaning and use of the curves is explained and derivation of the data employed is discussed.

A number of the terms used to describe mines and mine performance are peculiar to mine warfare or are used in mine warfare in a particular and limited sense. Those terms used to classify a mine by type and to describe its operational settings and data are defined and discussed below in order to clarify the data presented in this pamphlet. The sequency of listings in this glossary is the   same as that used in the preceding discussion of the data presented under the various headings.


Mines are classified as to type by their planted position, launching means, and firing method.


Planted Position. The positions are either bottom or moored. Bottom mines are generally limited to comparatively shallow water depths unless submerged submarines are the targets. Moored mines are generally used only in deep water.

Launching Means. Mines may be placed in position by aircraft, submarine, or surface craft. Aircraft planting is the primary method for conducting large-scale offensive operations involving replenishment of existing minefields. Submarine planting is used in offensive operations whenever planting secrecy is desirable. Surface planting is usually restricted to defensive mining in friendly or protected waters.

Firing Method . Mines may be fired either by contact, by influence resulting from proximity of a target or under the control of a shore operator. Contact firing is achieved either galvanic action (as the result of contact of dissimilar metals in salt water), or by simple closure of a switch as the result of the inertia of an impact. Contact firing is usually restricted to moored mines.

Influence firing is achieved by detecting physical changes caused by the presence or movement of a ship near the mine. U. S. Naval mines use magnetic, acoustic or pressure influence, or a combination of these. Use of magnetic influence involves either detection of the change in the magnitude of the earth's magnetic field as a result of the presence of a ship, or detection of the rate of change of field strength as a result of movement of a ship in the vicinity of the mine (also known as magnetic induction).

Use of acoustic influence involves detection of the low-frequency noise generated by a moving ship. The use of pressure influence involves detection of the pressure change resulting from displacement of water around the hull of a moving ship.

From the standpoint of countermeasures, magnetic influences are simulated readily, acoustic with greater difficulty, and pressure with extreme difficulty. The use of a combination of influences in a minefield or in a single mine complicates the problem even more.


Arming Delay. Arming Delay is the time required after water entry for a mine to be ready to detect the influence of a ship or to

  fire if contacted. Arming delay is provided for two purposes. Short periods of time, obtained by using clocks and soluble washers or arming cells, are used to provide safety in handling and planting mines. Long periods of time, obtained by using clocks, are used to provide tactical delay arming for sustained attrition mining as indicated in NWIP 26-1.

Sterilizing. Sterilizing is provided in mines to render them inoperative after a preset period of time. Sterilization is accomplished by long-period clocks or by electrolytic devices.

Ship Counts. Many mines are provided with ship counters (also called actuation counters). These devices may be set to require a certain number of complete actuations before a mine will fire. Ship counts are used to complicate sweeping operations, primarily in connection with sustained attrition minefields.

Firing Sensitivity. Firing sensitivity describes, qualitatively, the ability of a mine to respond to a given signal. Because most influence mines require combinations of actuating signals, timing periods, and rate of change as well as amplitude detection, firing sensitivity is generally impossible to describe in a simple, quantitative manner.

Timing Periods. Before the various timing periods involved in mine operation can be understood, it is necessary to understand the term "look". A look is defined as the event in the sequence of internal events required for the actuation of a mine that occurs when the influence or influences acting on the mine meet the acceptability requirements of the mine. The mine, in effect, senses the presence of a ship when a look occurs. For example, in Mine Mk 36 Mod 1, changes in magnetic field result in closure of contacts of a sensitive relay. Two closures of this relay must occur in order for the mine to be detonated, and these closures are called magnetic looks. It should be emphasized that the relay closure is a look, regardless of whether it results from the magnetic field of a ship, from a sweep, or from the force of an explosion.

The cycle of a mine is started by a look. It generally consists of a live period which incorporates one or more dead periods. A typical timing cycle is shown in figure 1 to illustrate the various periods defined in the paragraphs that follow.


Interlook Dead Period. The interlook dead period is the interval following an initial look during which production of subsequent looks will be ineffective. The use of interlook dead periods complicates sweeping in that it makes it necessary to generate two separate signals in order to cause two looks. Where the inter look dead periods available are long (of the order of ten seconds), the period also pro - vides some target selection since signatures with short transit times (i. e. , those of small, fast vessels) may be over before the end of the dead period, making it impossible to register the second look.

Time Out Period. The time out period is an interval peculiar to mines using A-6 type firing mechanisms. It is essentially the minimum period for which a pressure disturbance of sufficient amplitude must endure in order for a pressure look to be registered. The primary purpose of the time out period is to prevent pressure looks caused by short-period waves. From this standpoint, longer time out periods provide better protection against wave action, but such periods will also prevent

  response to ships with short pressure signatures (small, fast vessels).

Live Period. The live period is the interval following the look which initiates the mine cycle, during which the mine is capable of receiving the additional looks required to complete actuation. If the additional looks are not received during the live period, the mine then returns to its original condition. Where live periods may be adjusted to comparatively short times (about sixty seconds), they may exercise some target selection by preventing the receipt of the second magnetic look resulting from passage of large, slow vessels.

Intership Dead Period. When complete actuation of a mine results in a ship count rather than a firing, the ship count is usually followed by an intership dead period. This period is the time during which the mine may not start a new cycle of operation. The intership dead period is provided primarily to prevent rapid depletion of ship count settings by the passage of sweepers. The choice of setting generally depends on the sweeping operations anticipated.

Figure 1. Mine Cycle
Figure 1. Mine Cycle



The terms associated with depths and spacing of mines are self -explanatory. The terms associated with actuation data and damage effectiveness are peculiar to mining and require considerable explanation. In order to understand terms such as firing width, it is first necessary to understand the statistical nature of mine actuation.

Probability of Firing. When a ship passes in the vicinity of an influence mine, the mine may or may not be actuated, depending on such factors as the depth of the mine, the horizontal (athwartship) distance from ship to mine, the size and speed of the ship, the sensitivity of the mine, the heading of the ship, etc. Even if we hold all of these factors constant, and pass a number of ships of a given class at a fixed distance from the mine, only a portion of the ships may fire the mine because of the,, great variation in influence characteristics among ships that are nominally the same size. If we take a representative group of ships and sail them past a mine at various athwartship distances, the results of the various encounters may be plotted in terms of the percentage of ships which fired the mine (i. e. , the probability of firing) as a function of athwartship distance. A typical curve of this type is shown in figure 2, and applies to a specific mine type and sensitivity setting, to a specific planting depth, and to a specific target class and speed. Thus, to define the actuation capabilities of a single mine against several target classes and over a range of depths and speeds would require a large number of such curves.

Average Firing Width. The average firing width (w) is a numerical representation of the area under the firing probability curve. It is the arithmetic mean of the firing widths of all the targets in a class and, therefore, may be considered to be an actual width only in a statistical sense. Because of its statistical nature, many individual targets within the class will have firing widths smaller than w and many larger. Therefore, it may be erroneous to expect a particular ship to fire the mine within the precise distance specified as the average firing width. The use of w in the formulas of NWIP 26-1, is very meaningful since this doctrine is based upon mine attacks against all the ships of a given class.

Damage Effectiveness. As explained in Appendix C of this publication, the degree of damage obtained from an explosion of a certain

  weight of explosive depends on the depth of the mine and the athwartship distance from the target. To determine the damage which will result from actuation of a mine under a given set of conditions, some form of comparison must be made between the average firing width and the boundary of the damage zone of interest. This is not possible to do directly, since the shape of the probability of firing curve may vary from mine to mine or target to target. Figure 3 shows two typical probability-of-firing curves which have the same area, and therefore the same value of w. If both mines represented have the same damage capability, represented by zone boundaries -ydb and +ydb in figure 3, then it is obvious that mine A cannot be actuated by a ship passing outside the damage range, while a significant chance exists that mine B will be actuated at distances where damage will not be obtained. Stated differently, mine A will always produce the desired damage if it fires, while mine B will produce this damage only in a certain percentage of the times that it fires, and this percentage will be determined by the ratio of the area under the curve lying between -ydb and +ydb to the total area under the curve.

Figure 2. Firing Probability Curve


The total area under the curve has been defined previously as the average firing width. It is convenient to call the area lying between -ydb and +ydb the damage width, designated wdb. We then have two parameters defining the capabilities of the mine. The total probability of actuation is determined by the value of w, while the total probability of achieving the desired damage is determined by the value of wdb. The ratio, wdb/w, is the probability that, if the mine fires, it will yield the desired damage.   Damage widths can be computed for any degree of damage desired (heavy, moderate, etc.) by using the athwartship boundary of the desired zone as the value for Ydb. Because of the complexity of presentation, these widths are not included in this publication. They have, however, been used to determine the applicable coding for the tables of firing width. The codes included in the tables are based on the ratio of wdb to w, providing an indication of the probability of achieving damage if the mine fires.

Probability of firing vs athwartship distance
Figure 3. Typical Mine Firing Probability Curves


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