GERMAN INFLUENCE MINES WW II
HISTORICAL BACKGROUND. Germany was ready to introduce the influence mine when World War II broke out. Use of the magnetic mine achieved a degree of technical surprise and had considerable initial success until it could be recovered and analyzed. The Germans maintained an effective and versatile development program throughout World War II, and were considered the leader in the mine development field by the end of that conflict. German experience and know how has, and will continue to have, a marked effect on the mine development of all the major naval powers. The scope of the German mine effort during World War II is appreciated when we realize that the German Navy, during 1944, laid 24,698 influence mines in European waters.
TYPES. German influence mines included a wide variety of moored, bottom, and drifting mines capable of being laid by aircraft, surface craft, submarines, and swimmers. These mines exploited, in a wide variety of forms and combinations, the influence phenomena associated with magnetics, acoustics, and pressure changes which occur in the sea near moving ships.
DESIGNATIONS. German naval influence mines were designated by a series of three letters. The first two indicated the mine and its general type, the third letter indicated the model of that type. In the Luftwaffe, much the same system was used but the third letter was frequently replaced by numbers, see table 1.
During World II the allies established their own system of designating German mines. In the allied system, which may still be in use, two letters followed by numbers are used. The first letter is G for German. The second letter was arbitrarily assigned to a type of mine in sequence as that type became known.
Numbers following these letters indicated variations in type. Table 1 correlates these designation systems.
IDENTIFICATION.
PAINTING AND MARKINGS. Naval mines were painted overall black or dark green.
The Luftwaffe mines (Bomb Mines) were either light blue or light sand. The Germans commonly used a water soluble paint for their stenciled markings.
FEATURES. Typical identifying features of German mines are shown in figure 1 and figure 2. In general the German influence mine presents a smooth, rounded, external configuration having few protuberances and sharp angles. Most externally mounted parts are flush with the skin and are frequently protected, by flush cover plates. Parachutes or drogue chutes, used on many of the aerial laid mines generally remained attached if the mine fell on land. The bomb mines, frequently dropped without a parachute, penetrated deeply into the earth and left all indications similar to a large bomb. In general there was no external indication of the type of firing mechanism the mine contained. In a bomb mine, the tail dome
used gave a clue of the type; this method could not be relied on.
HAZARDOUS COMPONENTS.
The hazardous components are those associated with the main explosive system, the auxiliary firing system, and the protective devices.
MAIN EXPLOSIVE SYSTEM. This includes the main explosive charge of the mine, the booster system, and the detonator associated with the mine firing mechanism.
The Main Explosive Charge. The basic explosive used as the main charge is a mixture of HND, TNT, and aluminum powder, sometimes referred to as Hexanite. The mixture varies somewhat but generally approximates 13 percent HND, 63 percent TNT, and 24 percent aluminum powder. It is generally cast directly into the mine case
but may be block fitted in certain types. This explosive is very toxic and can cause severe dermatitis as a result of skin contact. An enriched mixture, high in HND, may be cast in the vicinity of the booster in certain mines.
The Booster System. The normal booster consists of a series of picric acid pellets which are arranged adjacent to the detonator to boost the explosive force to a point where the main explosive charge is reliably detonated. In some mines the booster is always in contact with the detonator while in others the two are
brought together by certain events that occur when the mine is laid.
The Detonator. Instantaneous acting electric detonators are used. In most instances a single detonator is depended upon. In some types of mines the detonator is assembled with, or as a part of a subbooster assembly. These compound device(s) are generally referred to as "gaines."
AUXILIARY FIRING SYSTEM. In aerial laid mines, an auxiliary firing system is provided to destroy the mine if it is dropped on land or in the water too shallow for it to function effectively as a mine. The devices used are special types of bomb fuzes having their own detonators and booster systems by which they explode the main charge when activated. The Navy types use a mechanical fuze; the
Luftwaffe mines use an electrical fuze. In both systems the fuzes begin to function on impact but are stopped or interrupted if the mine reaches an effective depth of water before their delay time runs off. In some types they restart and detonate the mine should the water pressure be reduced to less than a certain level.
PROTECTIVE DEVICES. German influence mines incorporate a variety of devices which are designed to detonate the main explosive charge, or a special destruct charge, if attempts are made to dismantle the mine, if the water pressure drops below a certain level, or if a buoyant mine breaks free from its mooring. Devices which protect the mine against stripping are sometimes referred to as PSE
(prevention of stripping equipment), a British term. A PSE device may include electrical switches, mechanical release devices, photoelectric cells, and electric cell forming devices; these will cause detonation if the mine is opened, light is admitted, parts are separated, or attempts are made to raise the mine from the
bottom.
EMPLOYMENT.
Germans used the influence mine with some initial success in a major effort to blockade British ports early in World War II. Mines were also laid from submarines in U.S. and Canadian waters, and in the Caribbean and off Panama. The influence mine was used extensively in European theaters as well as the Middle East and North Africa. The Suez Canal was repeatedly mined. As the German forces retreated they left the ports of Europe cluttered with influence mines as well as other types of demolitions and obstructions. This resulted in the formation of the allied "P party" organization, in which the U.S. played a part, whose function it was to clear captured ports of explosives.
DESCRIPTION.
TYPES. See Table 2 for the types of influence mines.
MATERIALS. The mines were made of nonmagnetic materials (to satisfy the requirements of the needle type magnetic firing mechanism). Most Navy influence mines were aluminum alloy. Wood and cement were used for some types of mines. Pressed paper was introduced near the end of the war but few paper mines were laid. The Air Force mines were nonmagnetic manganese steel.
SHAPE AND SIZES. The mines, depending on type, were made in a variety of shapes which included spheres, cylinders, hemispheres, cubes, or variations of these. The Luftwaffe mines were shaped like a bomb. The most common shape of the Navy influence mine was cylindrical. The sizes varied widely. Table 3 shows typical examples of shape and size.
FIRING PRINCIPLES USED. The Germans designated their firing mechanisms by letters to indicate type of operation followed by numbers denoting models of the type. The principles used to fire mines, together with their designations, are shown in Table 4.
5-6. These firing principles were used in combination of two or three; for example, DA = Pressure Acoustic, JDA = Induction Pressure Acoustic. In others, two variations of the same firing principle are used; for example, a sonic acoustic detector which, when activated, turns on a supersonic or subsonic system that must
be activated to fire the mine. Figure 3 shows a magnetic-pressure combination firing mechanism in a naval mine, and Figure 4 illustrates a German acoustic mine microphone.
DELIVERY SYSTEMS. German mines were delivered by surface craft, aircraft, submarines, and swimmers. In addition, river currents were sometimes used to deliver drifting mines to their target.
Surface Craft. Mines designed for laying from surface craft are normally fitted with wheels and are laid from mine tracts on the decks of the layers, Figure 5. In addition, many of the aircraft laid mines were adapted for laying by surface craft, Figure 6; great numbers were laid by German small patrol craft off the coast of England and off the south and north European coasts.
Aircraft. The naval aerial laid mines had severe speed and altitude
limitations in laying. The Luftwaffe desired a mine capable of being laid from higher altitudes and at greater speeds. As a result, the Luftwaffe embarked on their own development program which resulted in the BM series of mines. While the aerial mining was primarily directed to British waters, the entire coast line of
Europe, the Middle East, and North Africa were all mined from the air during World War II. The naval LM series of mines were also used against British cities during the blitz, utilizing their bomb fuze to detonate the mine after it came to rest on the surface. It was an effective blast weapon and much feared by the British populace. Figure 7 shows the bomb type mine in air flight.
Submarine. Two types of submarine laid mines are used: T type mines, laid from the standard torpedo tubes, and S type mines, dropped from special vertical tubes fitted in some submarines. In addition, the MTA mine was a true torpedo-propelled mine designed to be fired into harbors or other heavily defended areas. German submarine mining was conducted almost worldwide.
Swimmers. The KTMB mine was fitted with flotation gear and could be
maneuvered swimmers who, on placing it in position, deflated the flotation gear and armed the mine.
River Current. The Waserballoon is a drifting mine designed to destroy bridges, It fired when the shadow of the bridge fell on its optical firing system.
SPECIFIC INFLUENCE MINES. See Table 5 and Table 6 for naval influence mines and air force influence mines.
AUXILIARY DEVICES.
Arming Clocks.
1. UES Series Clockwork. Settable from 1/2 hour to 6 days. Started by starter plate which may incorporate an antirecovery switch.
2. ZE III Clockwork. Settable from 5 to 200 days. Used for either arming or disarming.
Ship Counters. Both mechanical and electrical types are used. Maximum settings vary with the type used; for example, the ZK II mechanical device can be set to 85 counts.
Sterilizers. A variety of clockwork sterilizers are available with maximum time periods as follows:
1. ZE I - 80 days
2. ZE II - 6 days
3. ZE III - 360 days
4. ZE IV - 45 days
5. ZE IV a - 60 days
6. Electrolytic cadmium cell sterilizer - 200 days
Pausenuhr. This is a clockwork device which operates over an 18-day period to turn the mine on and off at selected times once every 24-hour period.
Twelve Hour E. W. This is a test clock used in moored influence mines which tested the mine circuit for a 12-hour period. If the mine did not test satisfactorily, the clock scuttled the mine at the end of the 12-hour period.
FUNCTIONING.
ARMING. German influence mines make use of hydrostatic pressure, or the force of water impact, to start the process of arming. Some form of delay, most frequently a clockwork, is employed to permit the mine to stabilize in position before arming can occur. When magnetic needle type mines are used, arming time includes the period in which the mine adjusts its needle sensitivity in relation
to the earth's field. Arming consists essentially of preparing the electrical system of the mine for firing. The explosive system is usually aligned by the time the mine takes its position in the water. Arming can be long delayed but this feature is a countermeasure against sweeping.
FIRING. The mine is fired when a nearby ship, including a minesweeper, induces influence changes at the mine causing the firing system to go through an actuating cycle. The cycle results in the mine firing or the counting of one ship, depending on the ship counter setting existent when the actuation began.
COUNTERMEASURES RESISTANCE. German influence mines were made difficult to sweep because of:
1. Complex and multiple influence firing devices.
2. Delay arming.
3. Ship counters.
4. Periodic arming devices.
5. Mixed type mine fields.
STERILIZERS. Sterilizers were used to destroy the mine, or render it inert after a preset time has elapsed. The Germans used these devices to kill their old fields so their surface craft could return and lay fresh mines.
VARIATIONS. The use of the protective bomb fuze in the Navy's aerial laid mine permitted the use of these mines against land targets, and many of these mines were so used. In addition, some mines could be equipped with time firing mechanisms for use as simple time mines. In another variation, the mines could be equipped to fire by hydrostatic pressure directly and functioned in this method as a large depth charge. The use of mines in these roles was limited to specific special missions.
