Antisubmarine Warfare

In the period between the two world wars, of the various weapons used by the Regia Marina, the anti submarine ones were those which benefited the least from any technological improvement. In his official book “Organizzazione della Marina durante il conflitto” (Organization of the Navy during the Conflict”, Admiral Giuseppe Fioravanzo clearly states that between the end of World War I and 1936, the Italian Navy dedicated almost all of its resources solely to the development of ballistic weapons. During the conflict, ballistic weapons (guns) would be the least successful, while less conventional weapons, such as the “maiali,” scored the greatest successes.

Underwater bomb of the type BAS with a charge of 75Kg. of TNT – Museo Navale della Spezia, Italy
(Photo Cristiano D’Adamo)

At the beginning of the hostilities, enemy submarine activity was so minimal that not much attention was placed on the improvement of the few available weapons. Simply, the Regia Marina relied on defensive minefields and patrols conducted by torpedo boats equipped with depth charges and trailing torpedoes. The only unit specifically built for antisubmarine activities was the Albatros, laid down in Palermo’s shipyards in 1934.

Depth Charge
(Photo Cristiano D’Adamo)

The detection of enemy vessels, which up to the 30’s had relied solely on the use of a mechanical hydrophone (Tubi C also known as idrofoni meccanici) was substantially improved with the introduction of an electronic amplifier and headsets. Later equipment allowed for direction finding, a feature initially missing. In 1931, some units were also equipped with echofinders of the Langhiria-Florison type. Later evolution of this device would become standard equipment aboard torpedo boats and corvettes. These devices had a range of only 2000 meters and an error of up to one degree (0.3%).

Underwater bomb model de Quillac F/35t used in obstruction nets – Museo Navale della Spezia, Italy –
(Photo Cristiano D’Adamo)

Once localized, an enemy submarine would be attacked using B.T.G. (bomba torpedine da getto). These weapons would be either dropped or launched by the pursuer and, once in the water, would immediately sink under their own weight and then explode at a predetermined depth. Either a depth actuated switch or a timer actuated the trigger.

The principal models employed were the B.T.G. 100/1927 built by Moncenisio and loaded with 100 Kg. of TNT and a hydrostatic fuse (depth actuated). Predetermined depth settings were set at 25, 50, 75 and 100 meters. Another model, also by Moncenisio, was the B.T.G. 50/1917, 1927 with a charge of only 50 Kg, hydrostatic fuse, and setting for 20, 40, 70 and 100 meters. It is to be noted that there are historical references to lesser common models, such as the B.T.G. 50/1930, also by Moncenisio with a charge of 50 Kg and a diameter of about 30 cm.

The depth charges could be deployed by several means.

  • Tramoggia singola (Mud Hopper) Capable of launching a single charge
  • Tramoggia Multipla (Multiple Mud Hopper) Capable of launching a cluster of weapons at once.
  • Scaricabombe (Discharger) Capable of deploying a salvo of multiple weapons
  • Ferroguide (Railings) Railing for the spacing of weapons, practically capable of discharging the entire ordnance.

In the case of multiple launches, the charges would have different buoyancy, thus sinking at a different speed and therefore covering a greater area.

Pneumatic thrower 432/302 mm.
(Photo Rastelli)

Another weapon used by the anti submarine units was the towed torpedo of which several variances were available; notably the TR 1917, 1927, 1936, 1937 all having different weights and payloads. These weapons were towed by the unit at a depth ranging between 37 and 95 meters and would explode upon contact. Later models were equipped with magnetic fuses.
During the war, when the shortcomings of the antiquated Italian industry became evident, Italy began importing German weapons. These depth charges designated as W.B.D. had a charge of 125 Kg, while the W.B.F. had a smaller charge of 60 Kg. A thrower made by Krupp could deploy these depth charges easily and economically by propelling them upward and outward utilizing a small pyrotechnical charge These launching devices were known to be small, practical and highly reliable.

Discharger and towed torpedo on the R.N. Sirio

During the war the manufacturing company Laerte dell’Olio of La Spezia was contracted for the construction of new charges of 30, 100 and 150 kilos. New to the scene was also a thrower built by Menon of Roncade and used for the deployment of the German W.B devices which, unfortunately for the Italians, became in very short supply starting in 1942. Other companies involved in the research and development of new weapons were the Pignone, Bargiacchi and the already mentioned Moncenisio.