© Brooke Clarke 2017

    Time Line
Torpedo Description
Naval Mine Description
Hedgehog Description
Depth Charge Description


My interest in what I called outdoor intrusion alarms used in the Vietnam era led me to study Sonobuoys which are mostly used in Anti Submarine Warfare (Wiki: ASW).  Some of the technology used in a sonobuoy is the same as used in a torpedo, so I've started reading about them.  Torpedoes also make use of Gyroscopes as part of their guidance system and magnetic sensors (Sensors: magnetic, Flux Gate Patents) which are areas that interest me.

Reading about the problems of the Mk 14 Torpedo (Wiki) that made it pretty much useless for the first half of W.W.II got me interested in it's technical details.

The Wiki page lists the following problems:

  • It tended to run about 10 feet (3.0 m) deeper than set.
  • The magnetic exploder often caused premature firing.
  • The contact exploder often failed to fire the warhead.
  • It tended to run "circular", failing to straighten its run once set on its prescribed gyro-angle setting, and instead, to run in a large circle, thus returning to strike the firing ship.
I'm not sure that's correct.  It may be more accurate to say the Mk VI magnetic exploder failed to explode the torpedo under a variety of conditions and that occasionally it also caused a premature firing.

Time Line

This may be helpful to figure out which patents go with which devices.

1866 Whitehead Torpedo (Wiki) starts to be used
1892 Whitehead Mk 1 designed 1892, used 1894–1913
1892 Whitehead Mk 1B designed for E.W. Bliss production, used 1894–1922
1893 Whitehead Mk 2 designed for E.W. Bliss production, used 1896–1913
1893 Whitehead Mk 3 designed for E.W. Bliss production, used 1898–1922 (adds Orby steering Gyro)
1901 Whitehead Mk 5 designed, Mfg in UK, used: 1910–1922
1904 Bliss-Leavitt (Wiki) Mk 1 to Mk 6 designed, used: 1904–1922
1911 Bliss-Leavitt Mk 7 to Mk 9, used: 1912–1945 (Wiki)
1925 Mk 13 air or PT boat launched anti-surface ship torpedo, used: 1936–1950 (16,600 built)
1931 Mk 14 Sub launched anti-surface ship torpedo designed, used: 1931 to 1980 (13,000 made)
1938 Mk 15 destroyer launched anti-surface ship torpedo designed, used: 1938-1956 (9,700 built)
1940 Mk 17 heavy torpedo, not used

1942 Mk 19 Westinghouse follow on to the Mk 18 - only prototypes built
1942 Mk 24 "Fido" aircraft launched anti-sub torpedo designed, used: 1942–1948, (4050 built), made by GE & WE
1943 Mk 20 NTS Newport prototype sub launched
1943 Mk 16 sub launched anti-surface ship torpedo, used 1943–1975, (only 1,700 built)
1943 Mk 18 sub launched anti-surface ship electric torpedo, used 1943–1950 (9,000 built)
1943 Mk 21 Westinghouse attempt at the Mk 24 - only prototypes built
1944 Mk 34 Improved Fido aircraft launched anti-sub torpedo designed, used: 1948-1958, made by AMF, NOS Forest Park

Torpedo Description

The word Torpedo refers to an explosive that's in the water, so includes sea mines.  "Damn the torpedoes, full speed ahead" (Wiki) is in reference to Naval mines, not what we think of a torpedoes today.  The word also is used in conjunction with small explosive devices that are used on rail road tracks to a train.  The idea is that the first wheel on the engine will cause an explosion that can be heard over the noise.  These may be used in some pattern.  The "Bangalore torpedo" (Wiki) is a long explosive used to breach a barbed wire obstacle, like at the Normandy landing.

The automotive or fish torpedo is one that has its own propulsion.  Without propulsion it would be a sea or Naval mine.



Early torpedos were dumb.  That's to say they just ran in a more or less straight line.  But the more modern torpedos are designed for a specific task and to that end have an embedded strategy.  For example an early strategy for a torpedo designed to attack a surface ship would include a rule that it can not go below some depth so that it would not attack a firing submarine.  A converse strategy would be used for a ship launched torpedo designed to attack a submarine, i.e. it would always be below some depth that would protect the firing ship.

There are also strategies for search patterns of the torpedo does not detect a target and that strategy will depend on  the characteristics of the target, i.e. surface ship or submarine.
2341287 Torpedo controlling device, George Pookhir, Rubissow George A, Feb 8, 1944, 114/23 - 


This ranges from tens of pounds to a couple of thousand pounds of various explosives.  In one case any unused fuel is also "exploded" increasing the yield.  The destructive power of the explosive depends on its location relative to the target.  For example a torpedo hitting the side of a ship and exploding using a contact fuse is much less effective than the same amount of explosive detonating directly under the keel.
977438 Automobile torpedo, Gregory Caldwell Davison, Dec 6, 1910, - I think he saw the result of a shaped charge (Wiki) by placing the explosive behind the air tank, but that idea was not yet realized. The Bazooka (Wiki) was based on understanding how shaped charges work and came out in 1942.  This idea might have been good for torpedoes ramming the side of ships, but they soon worked by exploding under the hull.

Energy Source for propulsion

Whatever energy source is used to power a torpedo (or anything) it represents a liability in that if the energy is released at some time other than when it's wanted there's a big problem.  The more energy the bigger the problem.

In The Devil's Device (Ref 5) it's mentioned that the Japanese Type 93 Long Lance was powered by Hydrogen Peroxide although the Wiki page for the Type 93 says it was pure oxygen.  Some key specs: 24" diameter, 20,000 to 40,000 meter range at 58 to 39 miles/hr., 1000+ pounds of explosives, not bubbles since the products of combustion were CO2 (dissolves in water) and pure water.

The Howell Torpedo (Wiki) used the energy stored in a flywheel that started out at 10,000 PRM as both the energy source and acted as a gyroscope for maintaining a true azimuth.

311325 Marine Torpedo, J.S. Howell, Jan 27, 1885, 114/24; 114/122; 114/20.1; 114/22; 440/66  -
311326 Apparatus for Launching Torpedoes, J.A. Howell, Jan 27, 1885, 114/239 - Required to spin up flywheel.

The Whitehead Torpedo (Wiki) started out using a flask of compressed air to drive a piston engine.  (Note: it's very common to power model steam engines using compressed air).   Over time the technology to make compressed air containers improved allowing higher and higher pressures.  But the US was not able to make the high pressure air flasks.  (PS the US was not able to make a 1 arc second surveying transit like the Wild T1 during W.W.II)  The Bliss Co. bought rights to make the Whitehead torpedo.

693872 Propulsion of torpedoes, &c., by compressed air, Frank M Leavitt, Bliss E W Co, Feb 25, 1902, 114/20.1; 60/727; 60/786 - adds a heater for the air by burning liquid fuel
943833 Air-heater for automobile torpedoes, Frank M Leavitt, Bliss E W Co, Dec 21, 1909, 60/39.48 - improvement relating to the pressure of liquid fuel going into burner.
858266 Automobile torpedo, Gregory C Davison, US Navy, Jun 25, 1907, 114/20.1 -Curtiss turbine for Whitehead torpedo
1036082 Automobile torpedo, Gregory Caldwell Davison, Electric Boat Co, Aug 20, 1912, 60/39.91, 60/39.57, 60/39.53, 60/39.823 - burn oxygen and add water for steam.

 Later the air was heated using some fuel which increased the energy.  Later still water was added both to cool the engine and to get more energy from the steam.
Some Torpedoes were powered with what amounts to rocket fuel being used as a gas generator, but there were safety issues transporting the fuel.
There is a problem with the various types of air power, they leave a trail of bubbles in the water which traces a path back from the torpedo to the submarine that fired it.  Needless to say escort ships will quickly be attacking the sub.

Finally batteries were used with an electric motor.   Battery powered torpedoes do not leave any trail, so the escort ships do not know where to find the sub.
3005864 Sea water battery, Duncan T Sharpe, Bell Telephone Lab, Filed: Mar 29, 1945 (16 year delay) Pub: Oct 24, 1961 - maybe the Mk 18 torpedo (Wiki)

405196 Galvanic battery, John A. Barrett, J.A. Barret Battery Co., Jun 11, 1889 - chloride of-silver battery
1332483 Sea-water battery for vessels, Bridge Arthur, Mar 2, 1920 -
2176428 Secondary or storage battery, Kershaw William Ernest, Electric Storage Battery Co, Oct 17, 1939 -
2317711 Accumulator, Andre Henri Georges, Priority: Feb 4, 1936 Pub: Apr 27, 1943 -


The early engines were specially built, but were conventional piston designs (Wiki) used for steam/compressed air.  Turbines can also be used with compressed air, heated compressed air, or heated compressed air with water added to make steam.  Note that an air breathing Otto Cycle (Wiki) or Diesel Cycle (Wiki) engine will not work because there's no source of combustion air.  The Brotherhood Co. made a 3-cylinder radial motor that was used for many decades.

323270 Valve Gear, Peter Brotherhood (Wiki), UK, Jul 28, 1885, 91/353 - like all radial engines (Wiki) this one has an odd number of cylinders (3) but unlike aircraft radial engines that have overhead valves (Wiki) this engine has side valves, i.e. a flat head design (Wiki) making it smaller in diameter.

1152004 Fluid-pressure motor for driving torpedoes, Georges Henri Marius Canton, France, Aug 31, 1915, 92/70, 74/60, 92/71, 123/51.0AA, 123/56.6, 92/163 - maybe a swash-plate motor.  These offer inherent balance thus reducing vibrations.
Radial cylinder engine, Edward Jones Albert, Whitehead Torpedo Company Ltd, Dec 7, 1926, 91/481, 123/90.6, 91/185, 123/54.2, 91/331, 91/492, 92/72 - 4 cylinders in the first pancake then another similar pancake offset by 45 degrees making for a very compact engine (motor?).
3151527 Barrel engine, Hamlin Halley H, Clevite Corp, Oct 6, 1964, 91/507, 91/176, 74/60, 92/57, 91/503, 114/20.2 - wobble plate, low vibration design

858266 Automobile torpedo, Gregory C Davison, Jun 25, 1907, 114/20.1 - counter rotating turbine wheels cancel gyroscopic action so as not to interfere with stability.  An especially big problem when the torpedo is launched above the water.  The "balanced" design.
1088080 Driving mechanism for torpedoes, Frank M Leavitt, Bliss E W Co, 24. Feb 1914, 416/129, 416/171, 114/20.1 - 

Special fuels can be used where the fuel provides the oxidizer (Wiki).

Propellers or . . .

The early Torpedoes used a single propeller, but the problem is that tends to rotate the body of the torpedo in the opposite direction.  The first fix for that was to use coaxial counter rotating propellers or parallel shaft counter rotating propellers.  All of the above requires some type of gearing.  An alternate way is to make a special motor were the rotor and stator each have their own output shafts that are naturally counter rotating, but these may no be well balanced.  A similar turbine disegn may have been tried to get direct counter rotation.
2462182 Motor having coaxial counter-rotating shafts, Bluman John E, Guerdan Dikran A, Westinghouse Electric Corp, Filed: Nov 28, 1945, Pub: Feb 22, 1949, 310/115, 114/20.2, 417/69 - counter rotating coaxial output shafts

Starting with the Mk 48 Torpedo (Wiki) a Propulsor (Wiki) or is used instead of the counter rotating propellers.  One of the key advantages of this is reduced noise caused by the moving water.

Depth Control

There are a couple of problems with the hydrostat plus pendulum working together on the Uhlan principle.

1. The static pressure going to the diaphragm depends on the depth under water.  For sea water it's about 0.445 pounds per foot of depth.  But when the torpedo has forward motion the dynamic pressure at the diaphragm depends on both the depth of the torpedo and the
Bernoulli effect (Wiki) associated with the location of the diaphragm on the torpedo body.  The problem is that the diaphragm was located on the tapered tail section where, because of the Bernoulli effect, the dynamic pressure is lower than the static pressure causing the torpedo to sense a lower pressure than it should causing it to run deeper.

2. When gyroscopes are used in aircraft or ships for navigation it's important that they be located at the center of mass of the vehicle.  Other wise there is a lever arm acting between the center of mass and the location of the gyro that adds an error acceleration to the gyro thus causing an error.  I suspect that the same thing happened to the Mk 14 (and other) torpedoes if the depth setting pendulum location was not at the center of mass of the torpedo.

The Secret

881930 Immersion-regulator, Albert Edward Jones, Mar 17, 1908, 114/25 - pendulum v. pressure cylinder

1145355 Diving-gear for torpedoes, William Dieter, E.W. Bliss Co, Jul 6, 1915, 114/25 - Hydrostat and pendulum

899304 Immersion-regulator particularly adapted for torpedoes, Albert Edward Jones, Whitehead & Company,
Sep 22, 1908, 114/25 - "..a hdrostatic piston and a pendulum is employed".
Immersion-regulator particularly adapted
                        for torpedoes, Albert Edward Jones, Whitehead
                        & Company,

2604065 Depth control system for torpedoes, Elmer William B, Sec of Navy, Filed: Aug 31, 1945 (7 year delay) Pub: Jul 22, 1952, 114/25 - but is positioned on the sloping part of the tail = hydrodynamic problem.
Calls prior patents:
899304 see The Secret abvoe
1080116 Steering mechanism for automobile torpedoes, Frank M Leavitt, Bliss E W Co, Dec 2, 1913, 114/24, 114/25 - Hydrostat (K), pendulum (F) and Gyroscope (G) provide steering inputs.  again hydrostat is located on sloping part of tail = hydrodynamic problem..
1323347 Broaching Device for Torpedoes, L. M. Aspimwall, Westinghouse, Dec 2, 1919, 114/25 - causes the torpedo to broach (to break the surface from below) at the end of its run to make recovery easier when practicing.
1360325 Horizontal steering-gear for torpedoes, Simmon Karl A, Westinghouse Electric & Mfg Co, Nov 30, 1920, 114/24, 114/144.00R - Gyro
1370688 System of radiocontrol, Jr John Hays Hammond, Filed: Jan 22, 1914, Pub: Mar 8, 1921, 91/459, 342/423, 114/21.1, 91/464, 324/140.00R, 343/855, 91/465, 92/131 - Crude radio control of torpedo
1378291 Driving and governing means for torpedoes, Sperry Elmer A, Filed: Apr 2, 1915, Pub: May 17, 1921, 114/20.1, 114/23, 114/122, 114/24, 114/25 - not clear if only a pendulum is used for depth control - huge gyro takes up a lot of space.
1378740 Autogubernator, Thomas Walkup Samuel, Filed: Jul 30, 1917, Pub: May 17, 1921, 318/589, 200/183, 114/23 - depth is not mentioned
1532616 Equilibrating mechanism for flying machines, Erastus E Winkley, Filed: Jun 25, 1918, Pub: Apr 7, 1925, 244/177, 244/80, 185/29, 185/2, 244/14 - pendulum

2974623 Torpedo depth steering engine control, Ballou Jack W, Harvey Brooks, Filed: Aug 17, 1951, (10 year delay) Pub: Mar 14, 1961, 114/25 - "3. A depth control device for underwater vehicles comprising, in combination, a depth controlling means having a Uhlan principle type pendulum and hydro-diaphragm assembly linked to the valve of an air depth engine,..."  The Uhlan principle is mentioned in Chapter 4 The Afterbody and its mechanisms of OP 635 Torpedoes Mk 14 and 23 Types, 24 March 1945.

Depth control system, Eck Robert C, Sec of Navy, Filed: May 24, 1956 (6 year delay) Pub: Jul 24, 1962, 114/25, 367/95, 114/277 - prior art systems have +/- 3% depth error.  An increasing problem for depths of 1,000 feet.  Intended for towed submersibles, not torpedoes.

3393655 Gas steering and propulsion system for missiles, Eastman David P, Clevite Corp, Jul 23, 1968, 114/20.1 - Figure shows counter rotating props.  Pendulum & bellows for depth - mainly about using high pressure CO2 as control energy.

Navigation- Homing

The early torpedos were straight line devices.  Either the launcher was on a turntable and could be aimed or the ship needed to be brought to a heading pointing in the launch direction.  Note that the launch direction is not a line pointing to the target, but rather is the result of solving the target triangle (Wiki).  This triangle has sides proportional to the speed of the target and the speed of the torpedo where the solution is to aim the torpedo ahead of the target by the correct amount to get a hit.  The Torpedo Data Computer (Wiki: TDC) of W.W.II was a electromechanical computer that could solve the triangle and take into account the use of a settable gyroscope.

Later torpedos had settable gyroscopes (see a couple on my Gyroscopes web page) which allow firing the torpedo with the launching ship at any azimuth.  The output of the TDC is the gyro setting and for W.W.II or newer torpedoes can be set while the torpedo is in the tube ready to launch.  The gyro is constantly being updated so the time of launch is determined by the captain and not where the tube is pointing.
The torpedo will:
1. Run is a straight line for the "reach" distance, then...
2. make a turn with a known radius ending on the azimuth that was set into the gyro, then...
3. run in a straight line to the target, then...
4. if a modern torpedo with a strategy  misses the target it will search for a new target.
This means a torpedo can be launched from either a bow or stern tube toward a target at any azimuth.

The more modern torpedos (and some of the very earliest versions) use an electrical wire to control their heading.  In the more modern ones this allows the SONAR (Wiki) in the launching ship to be used to initially guide the torpedo to prevent the problem of the torpedo acquiring it's target using an active SONAR.  The latest torpedos have 2-way communication on the wire allowing the launching ship to see what the torpedo SONAR is seeing and thus help it lock on the correct target.

Another option is to replace gyroscopes with an Inertial Navigation System (Wiki).  Note that the drift of MEMs gyroscopes used in an INS is high but the run time between launch and the explosion of the warhead is measured in minutes so may not be a problem.

Starting with Fido, the Mk 24 Mine (Wiki) was an anti submarine torpedo that was the first to use acoustic homing.  The key problem was to minimize the noise generated by the torpedo itself.  This involved mechanically isolating noisy parts using gaskets including separating the warhead/sensor from the propulsion end.  But there remained the water noise similar to the noise a microphone experiences when it's windy.  The deeper the torpedo is the higher the water pressure and so the higher speed that's allowed on the propeller without cavitation (Wiki).

San Francisco Maritime org:  Torpedo Angle Solvers Mark 7 and Mods., Description and Instructions for Use

Gyroscopic Steering

621364 Device for starting torpedoes, Ludwig Obry, Mar 21, 1899, 114/24; 74/5.12  - applied to the Whitehead Torpedo (Wiki)
785425 Steering mechanism for torpedoes, Frank M Leavitt, E.W. Bliss Co, Mar 21, 1905, 114/24; 114/122; 74/5R - complains that the Orby gyro is delicate and hard to adjust.  gyro controls a SPDT switch which in turn controls electromagnets.
795045 Gyroscopic control apparatus, Frank M Leavitt, E.W. Bliss Co, Jul 18, 1905, 114/24; 114/21.1; 74/5R - general purpose gyro stabilized platform
839161 Steering apparatus for automobile torpedoes, Frank M Leavitt, E.W. Bliss Co, Dec 25, 1906, 114/24; 114/122; 74/5R - Leavitt gyro to replace the Orby gyro (Wiki)
894838 Gyroscopic steering-gear for torpedoes, Frank M Leavitt, E.W. Bliss Co, Aug 4, 1908, 114/24; 74/5.12 - ability to "set" the course prior to launching the torpedo
925709 Gyroscopic steering-gear, Frank M Leavitt, E.W. Bliss Co, Jun 22, 1909, 114/20.1; 114/24; 74/5.22 - easily removed gyro assembly
1030134 Automatic steering device for torpedoes, H W Shonnard, Jun 18, 1912, 114/24; 114/238; 74/5.12 - spin up gyro prior to releasing torpedo

Torpedo Data Computer (TDC) Patents

While reading The Devil's Device (Ref 5) the author never talks about the problem of guiding the torpedo to its target. By stating the speed and range of a torpedo (like the Japanese Type 93 (Wiki) makes is seem that makes it effective at that range, but as far as I know no torpedo has been effective at anywhere near that kind of range because there's has not been a guidance system that good.

The inputs to the TDC are the bearing of the sub and it's speed.  The bearing of the target from the periscope and the distance to the target from active SONAR (Wiki) pings.  Torpedo parameters like: dead time (from firing command to torpedo movement), torpedo speed, turning circle radius, "reach" distance, latitude where gyro calibrated &Etc.  The output is the gyro angle.

When the ideas from Ref 8 are taken into account the prediction of the target's position can have an error bar added depending on the predicted time between the fire command and the explosion of the torpedo.  Also based on these same ideas of energy maneuverability the characteristics of the torpedo and be optimized for its target list.

2022275 Device for indicating the position of ships, Davis Arthur Pattison, David M Mahood, Arma Eng Co., Filed: Nov 10, 1927, Pub: Nov 26, 1935, 73/178.00R, 114/144.00E, 340/988, 235/61.0NV - continuously computes the Lat and Lon of a ship by using it speed and heading.  A precursor to the TDC.
2406324 Gun control system, Pattison Davis Arthur, Arma Corp, Filed: Sep 6, 1933, Pub: Aug 27, 1946, 89/41.2, 318/595, 89/41.4 - aiming guns mounted on a moving ship trying to hit another moving ship is very similar to the problem solved by the TDC.  Arma Engineering worked on both problems.

2402024 Torpedo director, Crooke Raymond E, Ford Instr Co Inc, Filed: Jan 27, 1940, Pub: Jun 11, 1946, 235/403  - diagram shows torpedo making a 90 turn, is that always the case
2402088 Torpedo director, Ross Elliott P, Ford Instr Co Inc, Filed: Apr 29, 1940, Pub: Jun 11, 1946, 235/403 - includes curve in path due to gyro angle
2403505 Torpedo director, Crooke Raymond E, Ford Instr Co Inc, Filed: May 15, 1941, Pub: Jul 9, 1946, 235/403 - includes curve in path due to gyro angle, torpedo run distance (time) is an output,, patent includes equations solved.
2413846 Torpedo director, Ross Elliott P, Ford Instr Co Inc, Filed: Jun 20, 1941, Pub: Jan 7, 1947, 235/403 -
2911145 Torpedo director, Eugene Odin, Noel Urquhart, Bosch Arma Corp, Filed: Jan 28, 1939 (20 year delay), Pub: Nov 3, 1959, 235/403, 235/405 -

Acoustic Homing

114/23 Ship/Torpedo/steering  mechanism

2452068 Sound pickup device, Robert E Peterson, Submarine Signal Co, Filed: Jan 23, 1943, Pub: Oct 26, 1948, 367/150, 181/176, 367/165  
2382058 Torpedo, Hull Maury I, Aug 14, 1945, 114/23, 89/1.51, 318/480, 361/183, 244/190, 318/460, 367/133, 318/16, 114/21.2 - acoustic homing
2420676 Submarine signaling apparatus, Robert E Peterson, Submarine Signal Co, May 20, 1947, 114/23, 367/150, 114/21.1, 116/27, 181/402, 114/21.3 - torpedo application
2447639 Torpedo battery compartment, Daly Thomas A, Westinghouse Electric Corp, Aug 24, 1948, 114/20.1, 114/65.00R - Fido Mk 24???

2572116  Sectionalized torpedo, Daly Thomas A, Filed: Oct 7, 1946, Pub: Oct 23, 1951, 114/22, 114/21.1, 114/24 - Fido Mk 24
2615416 Variable enabler for acoustic torpedoes, Daly Thomas A, Gill Harry A, Sec of Navy, Filed: Nov 21, 1946 (6 year delay), Pub: Oct 28, 1952, 114/23, 200/38.00R - can set the turn on of the acoustic homing to start from 500 to 4000 Feet. - Fido Mk 24

2938486 Torpedo depth control system, Beatty Charles G, Daly Thomas A, Jones Leonard S, Osbon William O, Stephen, Soc of Navy, May 31, 1960, 114/25 -

2974620 Triaxial control system, Daly Thomas A, Malick Franklin S, Voorhees John C, Sec of Navy, Filed: Jul 15, 1953, Pub: Mar 14, 1961, 114/23 - El, Az & Roll

3228370  Electrical control systems, Daly Thomas A, Kowalyshyn Jr Stepben, Sec of Navy, Filed: Jan 28, 1950 (16 year delay) Pub: Jan 11, 1966, 114/20.1, 388/854 - Fido Mk 24??? - electric motor drive = no wake, battery voltage variation problem for tube filaments, slow speed for low noise OK for freightors (and subs)

3728982 Acoustic homing torpedo, R Dunlap, Us Navy, Filed: Jun 15, 1964, Pub: Apr 24, 1973, 114/23, 367/150, 114/21.1, 367/151, 367/96 -


The early torpedos just used a "contact pistol" (Wiki) that also included some Safe and Arm (Wiki) features.  For example a propeller at the nose that need to make some number of turns before contact can cause an explosion.  This would prevent a shipping accident from setting off an an unwanted explosion.

At the start of W.W.II the Mk 14 torpedo (Wiki)  used a magnetic influence exploder (Wiki: Magnetic Pistol) that should have triggered the explosion under the keel of a surface ship, but because, among other things, the depth control caused the torpedo to run about 12 feet to deep it did not work most of the time.  This was compounded by a defect in the contact fuse resulting in a very high number of duds for the first half of W.W. II.  The later Mk VI exploders included an improved metal ball contact exploder that worked at any practical contact angle.

I'm guessing that details on the exploder for each torpedo is part of the classified aspect since it does not show up in tabulated descriptions.

 Essentially the exploder was just a fluxmeter.  This is just a coil that senses the voltage generated when the magnetic filed changes.  The amount of voltage depends on the strength of the magnetic field AND how fast the field changes.  The polarity of the output voltage depends on the polarity of the magnetic field and the relative direction of motion between the target and torpedo.

A thyratron, such as the 2D21 (Valve Museum), will conduct when the grid No. 1 voltage exceeds 2 to 6 Volts.  One thing that might cause that is a vibration of the torpedo body and passing near a moderate magnetic filed either a target (but far from it) or not near any target but near a hunk of magnetized metal on the sea bed.

Mk 6-5  Exploder of 1945

The San Francisco Maritime organization has restored the USS PAMPANITO (SS-383) submarine and as part of that has on line manuals for a large number of it's systems.  OP 635, Torpedoes, Mark 14 and 23 Types, A Bureau of ORdinance Publication, 24 March 1945 includes the following photos of the Mk 6-5 Exploder along with a chapter on it.  Note the 1945 date, so NOT the Mk 6 that caused many problems.

The torpedo is shipped broken down into four parts:
1.  the nose that contains the exploder and explosives, or a training version
2. the compressed air flask
3. the afterbody or engine room which contains the combustion flask, dual stage counter-rotating turbine horizontal and vertical steering engines
4. the tail with the horizontal and vertical fins as well as the counter rotating propellers.

It appears that the Mk 6-5 exploder has the magnetic influence function active, but the books I've read say that it was deactivated for the last half of W.W. II.  What's the story?

The torpedo tube has provision to set the following parameters:

1. Gyro angle
2. depth
3. hi or low speed
My reading of the TDC function says it is constantly setting the gyo angle so that it's correct at the tome the torpedo is fired.
Fig 1 Cross section showing exploder location
Mk 6
                        Exploder Manual: Op 635 24 March 1945
Fig 2 bottom view of nose with exploder removed.
Mk 6
                        Exploder Manual: Op 635 24 March 1945
Fig 3 Exploder shown on bench with added legs to keep it stable.  Note The add-on ball switch trigger to replace the defective contact exploder.
Mk 6
                        Exploder Manual: Op 635 24 March 1945
Fig 4 Exploder showing the water channel and impeller used both for safe and arm as well
as DC electrical generation.
Mk 6
                        Exploder Manual: Op 635 24 March 1945
Fig 5 Exploder denator
Mk 6
                        Exploder Manual: Op 635 24 March 1945
Fig 6 Practice nose that ejects plywood disks when exploder fires.
Mk 6
                        Exploder Manual: Op 635 24 March 1945

Exploder (not rail road track signal, not oil wells, not barbed wire clearing)

420406 Submarine Ram and Torpedo Exploder, W.K. Cavett, Jan 28, 1890, 114/3; 114/19 -  maybe classes: 114/19; 114/18
2514359 Proximity fuse, Allison Malcolm G, Filed: Dec 28, 1945, Pub: Jul 11, 1950, 102/209, 324/257, 310/66, 102/212 - anti-aircraft, based on coil and rectifier (not a very good idea)
Torpedo exploder, John M Stockard, Filed: Nov 17, 1949, Pub: Jul 14, 1953, 102/226; 102/230; 102/416; 114/20.1 - Contact type, with Safe and Arm safety features.
1382374 Method and mechanism for exploding submarine mines, Hudson Maxim, Jun 21, 1921, 102/417, 114/20.1 - Iron sensor bar held in field of permanent magnet so the Earth's field is not a factor.
2397137 Magnetic controlling device, Glennon James B, Maltby Wilson R, Sellman Albert H, Filed: Jun 25, 1941, Pub: Mar 26, 1946, 340/850, 324/259, 340/551, 102/417 - magnetic needle held by PM. - sea mines

Mk 6 Exploder for the Mk 14 Torpedo.
2397678 Torpedo exploding mechanism, Minkler Chester T, Filed: May 9, 1932, Pub: Apr 2, 1946, 114/21.1, 102/427
  - works with Bronze or steel casing.  The Permaloy core sticks out of both ends of the 480,000 Turn coil.  (only 1 coil).
This is not a magnetometer, but rather just a pickup coil (11)  driving the gird of a triode tube with the trigger solenoid (20) in the plate circuit.

Mk 6
                                              Exploder for the Mk 14

2436394 Magnetic detector, Maltby Wilson R, Park Robert H, Filed: Jun 6, 1941, Pub: Feb 24, 1948, 102/417, 324/258, 336/90, 340/850, 336/233 - about the shape of the magnetic core of the sense coil.
2468968 Magnetic field strength indicator, Bell Telephone Labor Inc, Filed: Apr 20, 1943, Pub: May 3, 1949 324/246, 340/870.33, 324/253, 324/345 - 3-axis magnetometer
2477337 Magnetic Detector, William E. Kahl, Bel Labs, July 26, 1949 - mostly about sine wave coil drive and how even & odd harmonics come about
    2016977 Direction responsive system, Henry P Thomas, Gen Electric, Oct 8, 1935, 33/361, 340/870.32, 324/255 - aircraft magnetic compass
    2053154 Direct-current indicator, La Pierre Cramer W, Gen Electric, Sep 1, 1936, 324/99.00R, 336/87, 73/1.76, 324/254, 324/155, 336/110, 33/361, 340/870.33, 324/117.00R - 3-phase aircraft compass?
    2252059 Method and a device for determining the magnitudes of magnetic fields, Gustav Barth, Siemens App Und Maschinen Gmbh, Aug 12, 1941, 324/253, 102/427, 102/417, 340/870.33, 33/361 - Flux gates
    2415808 Detection of large magentic bodies, Oliver E Buckley, Bell Telephone Labor Inc, Filed: Jul 31, 1941, Pub: Feb 18, 1947, 324/67, 340/850, 324/243, 324/255, 324/345, 333/138, 340/870.33 - differential magnetometer for Submarine detection
2485931 Magnetic field strength indicator, Thaddeus Slonczewski, Bell Telephone Labor Inc, Filed: Apr 20, 1943, Pub: Oct 25, 1949, 324/247, 102/417, 340/870.33, 102/427 - 3-axis Earth's filed measurement.
2555209 Method and apparatus for measuring the values of magnetic fields, Gary Muffly, Vacquier Victor V, Gulf Research Development Co, Filed: Nov 1, 1943, Pub: May 29, 1951, 324/246, 324/345, 324/253,

2968242 Torpedo exploding mechanism, Erwood Beck Charles, Joseph Erwood, Wilbur Goss, Sec of Navy, Filed: Jun 20, 1946, Pub: Jan 17, 1961, 102/206, 102/212, 102/263 - battery powered, combined magnetic & contact.   Since filed in 1946 the torpedo must have been operational near that date.  Where used? Let me know.
Maybe for Fido Mk 24 (Wiki)?  used the "Mk 142 contact fuse"
Alternate torpedos might be the Mk 13 (Wiki) or
Cutie Mk 27 (Wiki) uses the
Mk 11 Mod 2 contact exploder
Firing means for torpedoes, Cleland Davis, Mar 2, 1909, - propeller on front for safety and Contact trigger
    1382374 (see above)
    2060198 Echo torpedo detonator, Hammond Jr John Hays, Nov 10, 1936, 114/21.2, 114/21.3, 102/211, 114/23, 102/418, 367/96 - active ultrasonic (20 kc) a clockwork switches the power to the transmitter or receiver so that the receiver is never on at the same time as the transmitter, so only a delayed/reflected signal will activate the receiver.
1518123 Exciting means for electrodynamical oscillators, Jr Harry P Lawther, Filed: Aug 29, 1918, Pub: Dec 2, 1924, 367/175 - Ultrasonic transmitter includes diaphram for underwater use
1625245 Receiving system for compressional waves, Dorsey Herbert Grove, Filed: Jun 22, 1918, Pub: Apr 19, 1927, 181/141, 367/130, 114/20.3, 367/902 - narrowbnad untrasonic receiver for underwater use
    2397678 Torpedo exploding mechanism (See above)
    2404553 (see above)

2972026 Damped inertia switch, Kendall James M, Filed: May 7, 1948 (13 year delay) Pub: Feb 14, 1961, -  maybe denator for Fido Mk 24
2993440 Control device, Chubb Lewis W, Prescott Herbert L, Sidney Siegel,Sec of Navy, Filed: Apr 6, 1945, Pub: Jul 25, 1961, 102/212, 102/417 102/212, 102/417 - Mk 18 Torpedo application, 2-coil gradiometer, bronze warhead for magnetic reasons.  1/2" dia rods with pure iron, threaded for balance, end caps, 200,000 Turns in each coil,

Naval Mine Description

Early Naval mines (Wiki) bristled with contact fuses and a ship needed to bump into the mine to set it off.  But later versions made use of magnetic influence exploders.  This led to anti-mining by use of man made magnetic fields or by use of wooden minesweeper (Wiki) ships.  Mining enemy harbors has been used as a way to deny the enemy supplies.  A blockade of the South was used during the U.S. Civil War (Wiki).  This was a very big thing for Japan in W.W.II.

The method of triggering a mine might be any combination of:
1. Mechanical contact
2. magnetic influence (Wiki: Influence Mine)
3. pressure - not weather or tides, but a heavy ship
4. gravity - not tides or small boats, but a heavy ship
5. Sound
6. AC Impedance

It was the experience gained with Naval Mines in W.W. I that the effect was much larger when the mine exploded under ship and broke the keel that led torpedo designers to come up with a magnetic influence exploder.

Another countermeasure for magnetic influence mines is Deguassing a ship (Wiki) so that it's less likely to set of the mine.

A Counter countermeasure is for the mine to include a counter so it does not explode on the first magnetic anomaly, but after many.  So a man made magnetic field is unlikely to set it off.

San Francisco Maritime Org
Ordnance Pamphlet No. 898 Mine Identification, October 1943 -
Operational Characteristics of U.S. Naval Mines (U), ORD 696(B), 1959,
Mine Disposal Handbook, 1945

571739 Electromagnetic sentinel, Francis B. Isadt, Nov 24, 1896, - an iron core coil is excited with an AC signal and when an iron clad ship is nearby the impedance change shows it's presence.
1390768 Submarine mine, Grove Dorsey Herbert, Filed: Dec 14, 1915, Pub: Sep 13, 1921, - spherical, replaces trigger wire from shore with underwater acoustic signal using tuning fork.

1491004 Explosive mine, Duffie John J, Us Government (Berkeley, Calif.), Filed: Nov 18, 1918, Pub: Apr 22, 1924, - combines a microphone and clockwork so loud sound needs to be present for more than an instant.

1295051 Drifting mine, Chester T Minkler, Us Government, Feb 18, 1919, 102/422 - includes provision to sink after some Sal Ammoniac (Wiki) dissolves.
1538316 Explosive mine, Duffie John J, Filed: Feb 8, 1918, Pub: May 19, 1925, - loud sound waves set it off, uses a meter movement with contacts on needle.

2431319 Magnetic firing device, Ellwood Walter B, Filed:Feb 9, 1943, Pub: Nov 25, 1947, - versions for both the ash-can and Mk 9 depth charge

2881702 Mine firing mechanism, Glennon James B, Hobbs Charles A, Maltby Wilson R, Park Robert H, Filed: Aug 9, 1941, (18 year delay) Pub: Apr 14, 1959, - looks for change in magnetic field with time matching a ship and so can discriminate against mine sweeping man made magnetic fields.  Uses telephone stepping relays

2892402 Gravity controlled mine firing mechanism, Park Robert H, Filed: Dec 8, 1941, (13 year delay) Pub: Jun 30, 1959, - not effected by tides or small craft, but triggers when heavy ship is nearby. (see my page on Gravity meters, which lists Wright Gravity Meters under Historical - spring suspended mass
2892403 Mine firing mechanism, Edward S Gilfillan, James B Glennon, Robert H Park, Iii Elihu Root, Filed: Sep 18, 1941, (18 year delay) Pub: Jun 30, 1959, - combines sound, pressure and magnetic influence.

Deepwater target-seeking mines, Glen T. Lampton, Sec of Navy, Filed: Dec 28, 1959 (22 year delay ), Pub: Jun 23, 1981, 102/418, 102/411 - looks like torpedo, but does not have any power unit.  Propelled from bottom by bouncy and steered by sound.

USS Princeton (CG-59) 1991 mine (Wiki) damage.

Hedgehog Description

The Hedgehog  (Wiki) is a spigot mortar (Wiki) mounted on the bow of a ship, aka: Anti-submarine Projector.  They were fitted with contact fuses on the front end so only would explode if a direct hit on a submarine (or the ocean bottom?).   After all the mortar shells have been launched the launcher has the appearance of a Hedgehog or Porcupine.  They weigh about 30 pounds each.

Depth Charge Description

Early depth charges (Wiki) were called "ash cans" because that's what they looked like, i.e. a cylinder with flat ends.  The bunghole (Wiki) was replaced with a fuse the could be set for the depth at which it would explode.  One of the problems with the "ash cans" was that they went down slowly with the centerline approximately horizontal and so a submarine could escape before they got to depth.  The Mk IX depth charge was designed for rapid decent (centerline approximately vertical) and has optional spoiler plates so it can also have controlled slower rates of decent.

Depth charges can be rolled off a rack and dropped overboard or they can be projected using a sort of mortar to throw them some distance from the ship.

San Francisco Maritime org:
Depth Charge, Mark 9 and Modifications, OP 866, 1944, covers the fast sinking U.S.N. depth charge of WW II.
The Mk 1 Mod 1 firing pistol can be set for: 50, 75, 100, 150, 200, 300, 400 or 500 feet.
Depth Charges, Mark 6, Mark 6 Mod. 1, Mark 7, Mark 7, Mod. 1, OP 747, 1943, covers the U.S.N. depth charge from the first half of WW II. - this is the "ash can".  The possible depths for the Mk 6 pistol are: 30, 50, 75, 100, 150, 250 and 300 feet and the Mk 6-1 pistol adds a 600 foot setting.

2641184 Streamline depth charge, Booth Seth W, Park Robert H, Royal Weller, Russell Arthur G, Filed: Aug 25, 1942, Pub: Jun 9, 1953, 102/391, 340/850, 102/417, 367/93, 324/257 - This is the Mk 9 fast decent depth charge used in W.W. II.  mentions 2962966.
2962966 Firing control circuit, Gieseler Luther P, Filed: Apr 18, 1946, Pub: Dec 6, 1960 (14 year delay), 102/391, 102/417 - magnetometer magnetic influence fuse (see Fluxgate Patents) for depth charge.

Patents Published Nov 29, 1960 with sequential patent numbers (many with many years delay because of classification)

2961954 Depth charge firing mechanism, Axelson Carl A, Moore Harry H, Stearns David M, Stresau Richard H F, Filed: Feb 1, 1943 (17 year delay ) Pub: Nov 29, 1960  -  depth, time and magnetic influence combined.
2961955 Depth charge arming device, Macdonald Waldron S, Filed: Feb 11, 1946 (14 year delay), Pub: Nov 29, 1960, - 

2961956 Arming mechanism for a depth charge, Townsend Richard W, Filed: Jan 6, 1947,  (13 year delay) Pub: Nov 29, 1960, 102/392 - can only arm after a preset depth, can deactivate below some preset depth, does not respond to rapid pressure changes (like nearby depth charges going off), includes some time delay elements in the arming function, Fig 16 shows a magnetic influence trigger that is only connected to the batteries after a preset depth is reached.  When the next preset depth is reached the arming circuit becomes active (maybe allowing time for the vacuum tubes to warm up).  Cites prior French and Italian patents.

2962966 Calls:
1310568 Acoustically Operated Contact Actuating Mechanism and System Employing the Same, A.C. Heap & A.B. Field, UK, July 22, 1919, 102/418, 114/240.00R, 367/135 - submarine triggers mine
1382374 Method and mechanism for exploding submarine mines,
1448976 Submarine mine, Palmer Wayne F, Mar 20, 1923, 102/417 - Magnetic influence, ompass needle with counter mining and self setting features
1538315 Thermomicrophonic firing device for submerged mines, Duffie John J, U.S. Government, Filed: Aug 9, 1917, Pub: May 19, 1925, 102/418, 367/133 - acoustic trigger with timer to allow installation
2341351 Aerial mine, Barkley Joseph Amos, Filed: May 15, 1941, Pub: Feb 8, 1944, 102/405, 361/189, 327/516, 361/170, 244/31, 102/211, 361/182, 367/135, 244/87 - acoustic to be triggers by nearby aircraft (not very practical)
2404553 Electric fuse and setting apparatus, Wales Jr Nathaniel B, Filed: Aug 6, 1941, Pub: Jul 23, 1946, 102/219, 89/6, 315/227.00R, 327/100 - artillery shells
2404806 Submarine detector, Lindsey Henry A D, U.S. Army, Filed: Mar 19, 1942, Pub: Jul 30, 1946, 340/850, 102/402, 324/247, 324/331 - MAD (Wiki) towed by aircraft
Split: 2379447 Anti-submarine Device, Lindsey Henry A D, U.S. Army, Filed: Mar 19, 1942, Pub: Jul 3, 1945, 102/417, 102/212, 340/551, 324/247, 324/67, 307/652, 324/258, 340/552 - Very similar to the device in 2404806 except the part that was in the aircraft is now floating on the ocean surface and the MAD detector is now suspended underwater some distance.  When the magnetic field of the submarine motor battery circuit is sensed it fires a small charge allowing the submerged mine to fall in the water and when at a predetermined depth it explodes.
2961957 Anchor release for a moored drill mine, Sylvan Wolf, Sec of Navy, Nov 29, 1960, - for training

2961958 Thermal controlled arming device for a mine, Brown Ellis M, Toomey John F, Filed: Mar 8, 1944, (16 year delay), Pub: Nov 29, 1960, - A large mechanical impulse (dropping the mine) can cause it to explode so this version uses a fusible alloy that melts to arm the mine.  Also includes a sterilization feature to deactivate the mine.

2961959 Torpedo actuating lanyard seal, Lewis H Van Billiard, Gen Electric, Nov 29, 1960, - pull lanyard through watertight gland to activate torpedo
467792 Submarine Shell,
George Frank Elliott, US Navy, Jan 26, 1892, - anti mine sweeping device.
Arming device for torpedo exploders, Dinsmoor Theodore E, Jun 5, 1956, - prevents assembly with actuator in the armed position
2961960 Torpedo exploder mechanism, Bob Norris, Kendall James M, Filed: Jul 20, 1949, (11 years delay) Pub: Nov 29, 1960, - Fido Mk 24 Exploder  - time at depth needed to arm, triggered by inertia (contact) switch, sterilize at 500 feet
1121563 Automatic Steering Apparatus, Karl O. Leon, Dec 15, 1914 - sound based
2954734  Torpedo Exploder Mechanism James M. Kendall, Filed:Oct 17, 1947 (13 year delay) Pub: Oct 4, 1960 - does not work well with homing torpedoes because it makes noise
1892431 Echo torpedo, John Hays Hammond, Jr (Wiki)), Filed: Apr 2, 1928, Pub: Dec 27, 1932, - active SONAR
2419815 Water armed fuze, Breeze George E, Gay Godwin R F, Filed: Oct 3, 1944, Pub: Apr 29, 1947, - uses water activated battery
2961961 Torpedo exploder mechanism, Holdrege Charles F, Kendall James M, Filed: May 26, 1947 (13 year delay), Pub: Nov 29, 1960, - for submarine launched acoustic homing torpedo aimed at surface ships - special provisions to allow for broaching (jumping out of the water and returning).
1121563 (see above)
1137222 Torpedo and other submarine apparatus, Karl O. Leon, Leon Steering Device Company, Filed: Feb 11, 1908, Pub: Apr 27, 1915 - acoustic "...what I term a hydrophone..." (did Karl coin the word hydrophone)
1312510 Sound-controlled dirigible torpedo, George Baker, Aug 12, 1919 -
2419815 Water Armed Fuse (See above)
2961962 Trip-wire flare, Jackson Leonard D, Filed: Jan 19, 1945, (15 year delay), Pub: Nov 29, 1960 - I know used in Vietnam, but W.W.II?

2399248 Depth charge projector, Gebhard Edward P, Patrick Jr William E, Filed: May 27, 1942, Pub: Apr 30, 1946 - YouTube video showing its use with Mk 9 depth charge.



 Gyroscopes - used to keep torpedo going in straight line

Flux Gate Patents - many of the single coil type were for Naval Mines.

DC Gaussmeter Model 1, Helmholtz Coils, GE Gauss Meter, AMY6 Polarity Tester
HT20 2000 mT Magnetic Flux Meter - this instrument has very similar capabilities, bur for a much lower price
Sensors - Magnetic - Helmholtz Coil
Telephone patents
Electromagnetic devices:
Electromagnetic Toy Engine
Gilbert DC 3-pole Electro-magnetic Machine
Leclanché Battery - wet cell
MESCO 1011 Toy Engine
No. 6 Dry Cell -
Toy Motor Kit & modern version as well as Science First demonstration motor -
Vibrators -
Weeden DC 2-pole Electro-magnetic Machine -
Walker Scientific MG-3D Gaussmeter -
DC Permenant Magnet Motors
Walker Scientific MG-3D Gaussmeter


Ref 1: Hellions of the Deep: The Development of American Torpedoes in World War II by Robert Gannon
Ref 2: Ship Killers: A History of the American Torpedo by T. Wildenberg & N. Polmar, 2010 -
Ref 3: Iron Men and Tin Fish: The Race to Build a Better Torpedo During World War II by Anthony Newpower
Ref 4: Weapons That Wait: Mine Warfare in the U.S. Navy by Gregory K. Hartmann, 1991
Ref 5:
The Devil's Device: Robert Whitehead and the History of the Torpedo by  Edwyn Gray
Ref 6:
Torpedo: Inventing the Military-Industrial Complex in the United States and Great Britain by Katherine C. Epstein, 2014 - the quest for better torpedoes led to the military-industrial complex
Ref 7: The influence of Seapower on History 1660 - 1783 by Captain A.T. Mahan, USN (Wiki)
Ref 8: Boyd: The fighter pilot who changed the art of war by Robert Coram, 2002 -
Energy–maneuverability theory (Wiki) for aircraft dog fights


The Torpedoes of WWII Documentary - 46 minutes


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