With the generic term of mine, the Regia Marina classified a series of static underwater weapons designed to explode upon contact with the hull of a ship. Later, this definition was broadened to include all new triggering mechanisms which, instead of physical contact with the target, were activated by magnetic influence, acoustics or water pressure.
Mines evolved dramatically during the beginning of the century when a laborious manual deployment process was replaced by an automatic mechanism which would precisely deploy the weapon. One of the Italian pioneers in this area was Emanuele Elia (1866-1935), a Lieutenant in the Regia Marina who, after leaving the Navy, dedicated himself to technical studies. Another pioneer was Admiral Gerolamo Bollo (1866-1931), a specialist of underwater weapons. During World War I, Bollo and Elia mines were equally used and both models were substantially improved.
In 1936, the Regia Marina introduced the P 200 built by Pignone(1) of Florence. This was a much-improved model which, after the beginning of the hostilities, would be further modernized by the introduction of the antenna(2), thus greatly improving its effectiveness. At the beginning of the hostilities, Italy had almost 25,000 mines distributed amongst several naval bases from La Spezia to Massawa. As with many other ordnance and war material in general, these weapons were not available in sufficient quantities and, later in the war, Italy had to resort to German mines.
Italy entered the war with the following models:
Elia V.E. (Vickers – Elia) with 145 Kg of explosive.
Bollo Type B with 125 Kg of explosive, later increased to 130 Kg.
P 200 Pignone with Kg. 200 of explosive.
Coloniale P 125 similar to the P 200 but with only 125 Kg of explosive and a maximum depth of 200 meters. Specifically built for tropical waters with a greater buoyancy to allow for the formation of barnacles
C.R. (Reduced characteristics) Similar to the P 200 but with only 150 Kg of explosives, a maximum depth of 200 meters and only two settings, 4 and 9 meters.
T 200 (Tosi) used by submarine of the classes Atropo and Bragadin.
P 150 used by submarines of the class Foca
Also available were some older models, mostly left over from the previous war:
Harlè a French model with a charge of 100 Kg.
C. 15 an Austrian model also with a charge of 100 Kg.
In February 1941, following the conference of Merano, Germany began providing the Regia Marina with several shipments of mines of the following models:
These last ones were of the very effective magnetic type. In total, Italy received 12,224 German mines.
Mines were generally of two kinds: moored and ground. The moored mines were designed to operate at a predetermined depth, while the ground mines would lie on the ocean floor. It should be noted that a drifting mine would be nothing else but a moored mine which had lost its anchor, and that the Regia Marina did not intentionally employ any such device. Some British sources report the existence of two Italian drifting mines, the IN and IO, but no reference can be found in the official Italian documentation.
Mines were usually activated on contact. Most moored mines were of this kind. The mine, usually of spherical dimension, was equipped with spikes, called hertz horns which, once touched, would cause the weapon to detonate. Later, following the example of other navies, the Regia Marina introduced mines which could be remotely triggered by a nearby magnetic field, sound or change in water pressure. Some special purpose mines were also produced and they were designed to operate for a determined period of time and then self-destruct. Magnetic mines were activated by the magnetic field of a ship, also known as the magnetic signature. This force was relatively miniscule, usually around 50 milligause, but tended to be similar amongst different kinds of ships.
To provide for defense against this new kind of weapon, the Royal Navy experimented with a degaussing system first employed on the cruiser Manchester and later on the passenger ship Queen Elisabeth. Later, British scientists developed several mine sweeping technologies including, an airborne one installed on Wellington bombers, which was used to remove German mines from the Suez Canal.
The moored mine represented the vast majority of the type used. The depth of the weapon would be configured based on the intended target. An anti-submarine mine would usually be placed between 8 and 9 meters, while an anti-ship one would be moored between 3 and 4 meters from the surface of the water. The mooring cable could extend up to 800 meters from the ocean floor. The low tide of the Mediterranean would facilitate the accuracy of these settings. Mines were susceptible to bad weather conditions and the most common failure was the breakage of the mooring cable. The resulting drifting mine could easily float for over a year and then succumb to the weight of the marine vegetation which would inevitably form around it, causing it to sink.
Mines were laid both defensively and offensively, and usually anti-submarine mine fields required less powerful charges. These fields could assume several shapes, from single line to a serpentine, parallel lines or multiple lines at various intervals. Most of the older models were used defensively, while the P 200 was the primary offensive weapon. Submarine-laid mines, due to the unusual delivery system, were slightly different and, employed additional safety devices such as the “salt of ammonia” safety pins which, once dissolved in salt water, would activate the weapon.
For the deployment of mines, the Regia Marina employed several units, from ferry boats, to mine-layers, from submarines to cruisers. Most units were equipped with removable railing. Mines were equipped with small casters, which would fit these railings, thus easing the process of pushing the mines towards the stern of the ship from which they were usually deployed. This mechanism was not fool proof and many derailments were actually reported. With the introduction of German mines, the original Italian railings had to be modified to support these new mines which had a different gauge. It is reported that the Germans demanded that the removable railing be welded, thus reducing the possibility of derailment. Naturally, welded railing could not accommodate Italian mines.
All mines were properly marked with a unique serial number to allow for quick identification. A mine found adrift would first be identified and then exploded. Using the serial number, naval authorities could identify the origin of the weapon and eventually restore the minefield. Mines are non-discriminatory weapons which could easily strike friend and foe alike. Italian minefields were in general accurately mapped and, especially at the beginning of the conflict, properly advertised.
The successes of both the defensive and offensive fields deployed during the war should be considered adequate. Quite relevant is the large number of British submarines sunk by Italian mines. Also relevant is the fact that the famous Malta-based H force was nearly destroyed by an Italian minefield.
(1) Founded in 1842 as a foundry, it is currently known as “Nuovo Pignone” and fully owned by GE.
(2) A remote triggering device.