Pola - 1918, affondamento della corazzata "Viribus Unitis"
Alessandria - 1941, affondamento della corazzata "Queen Elizabeth" (Siluro Lenta Corsa detto "Maiale")
Genesis of the design
In October 1935 two engineer officers, Sub-Lieutenants Teseo Tesei and Elios Toschi submitted plans for an improved version of the Mignatta to Admiral Cavagnari, Chief of the Supamarina, the Italian Naval Staff. Cavagnari approved the idea and work began at La Spezia. Three months later the prototypes were ready. Toschi described the craft as:
... in reality a miniature submarine with entirely novel features, electrical propulsion similar to an aeroplane ... The crew (pilot and assistant) instead of remained closed and more or less helpless in the interior, keep outside the structure. The two men, true fliers of the sea-depths astride their little underwater aeroplane, are protected by a curved screen of plastic glass ... At night, under cover of darkness and steering by luminous instruments, they will be able to attack the objective while remaining invisible to the enemy . . . They will be able to cut nets and remove any obstacle with compressed air tools and reach any target. . . with long range breathing sets they can operate at depths down to 30 meters and can carry a powerful explosive charge into an enemy harbour. Invisible and undetectable by the most sensitive acoustic detectors, the operator will be able to penetrate inside the harbour and find the keel of a large ship, attach the charge to it and ensure an explosion will sink the vessel.
There was, however, no requirement for such a craft in Italy's Abyssinian adventure so the weapons were stored and their crews assigned to other duties. But by the summer of 1939 it was clear that a European war was imminent, so the 1st Light Flotilla was formed in June under the command of Capitan di Fregatta Paolo Aloisi with instructions to:
... train a nucleus of personnel for employment with given special weapons and of carrying our ... experiments and tests concerned with perfecting the said weapons.'
Aloisi was succeeded in command by Capitan di Fregatta Mario Giorgini on the outbreak of war who in turn was succeeded by Capitan di Fregatta Vittorio Moccagatta in March 1941. Under Moccagatta's leadership the organization ceased to be part of the 1st Light Flotilla and became the 10th Light Flotilla, Decima Mas, in its own right. This is the name by the which the unit will be referred to in these pages. Moccagatta further split Decima Mas into two parts: a surface and a sub-surface weapons group. The former dealt with the operation of the fast explosive motor boats, and the latter with human torpedoes and Gamma assault frogmen.
A base was established on a secluded stretch of land on the Boca di Serchio and the officers and men involved in the initial tests were recalled from their units. Cavagnari had taken the decision to order twelve prototypes and at the beginning of 1940 the first successful exercises were held, with the old cruiser Quarto as the target, in the Gulf of La Spezia. These were successful and although two of the craft broke down, the third attached a dummy charge to Quarto which would certainly have resulted in her destruction. The concept had become a reality. However, the loss of two years' research and development time meant that when Italy declared war on 10 June 1940, the weapon was still in an experimental stage and few were available for operations.
Construction and machinery
What was the craft which Decima Mas was to operate so successfully? It was officially known as Siluro a Lenta Corsa (SLC) but the name by which they will be forever be known is Maiale (`Pig'). During early trials Tesei had to abandon a sinking SLC and came to the surface with the words, `That swine got away!'. The name stuck. The craft was 7.3m long overall which included the 300kg warhead at the front which was 1.8m long. The diameter of the craft was 0.53m. The two operators sat astride the craft, the driver in front with the No.2 behind. Beneath the driver's seat was the forward trimming tank. Between and beneath the two seats was the battery consisting of thirty 60v cells. At a speed of 4.5kts the Maiale had a range of 4 miles and at 2.3kts 15 miles.
Inside the after portion of the craft was the l.lhp (later increased to 1.6hp) electric motor and the stern trimming tank. At the stern was the propeller, with hydroplanes and a vertical rudder, both surrounded by a protective shroud.
The two operators sat behind shields to lessen the water resistance. The driver controlled the craft by means of a joystick which worked both rudder and hydroplanes. Speed was regulated by a fly-wheel connected to a rheostat. Between the two operators was the quick-diving tank which was flooded by lever action from the No.2's position and blown by compressed air from a compressed air cylinder. Behind the No.2's seat was a locker containing net cutters, a set of working tools, plenty of rope and clamps used to attach the warhead to the hull of the target. The operators wore a one-piece `Belloni' suit and breathed oxygen through a closed-cycle breathing apparatus (Autorespiratore ad Ossigeno) which left no tell-tale trail of bubbles on the surface. The apparatus consisted of two high-pressure oxygen cylinders which gave about 6 hours' breathing time. The oxygen was fed, via a reducing valve and a flexible tube, into the operator's mouthpiece. The operator exhaled through the same tube and the `exhaust' air was cleaned in a cylinder containing soda lime crystals.
The 300kg warhead (some later Maiale could carry two 150kg charges) at the front of the craft was held in position by a metal clutch. The procedure for attaching the warhead to the target was for the driver to position the Maiale directly under one of the target's bilge keels. The No1 would then dismount and secure a clamp to the keel to which was attached a length of rope. The driver would then move the Maiale forward under the hull while the diver swam round and attached another clamp to the bilge keel on the other side of the hull. He would then return and attach both cables firmly to the warhead and set the fuse -a setting of 21/2 hours delay was possible. When all was secure, he would give the appropriate signal and the driver would release the warhead, so that it hung under the target's hull, suspended from the bilge keels. The operators would then get clear.
Initially the Italians thought of delivering the Maiale to the operational area by air using a Cant Z.511 flying-boat. This idea was swiftly abandoned, although it is interesting to note that in turn the British and Germans both considered the possibility of delivering underwater assault craft by air. Instead Aloisi turned to the submarine as the most likely means of delivery. The old boat Ametista was fitted with pressure-tight containers on her casing in which the Maiale would be kept on passage. When the submarine was near the target area, the Maiale would be removed from the containers and released to proceed on their own. Following the success of trials with Ametista, three such containers were fitted to the submarines Iride, Gondar, Scire and Ambra. Initially the submarine would surface to launch the SLCs, but the Italians quickly developed quite sophisticated exit/re-entry techniques so that the operators would leave the parent boat through the fore hatch while it was sub-merged. This, of course, reduced the risk of the boat being caught on the surface with the containers open and the Maiale and their crews on the casing. An important feature of the Maiale containers was that they were built to the same constructional standards as the submarine's hull so that the commanding officer would not have his freedom of action constrained a specially converted motor boat, Motosiluranti. Two such MTBs were converted and could carry a Maiale on a specially-configured stern ramp, from which it would be slid into the water stern first.
A feature of Maiale operations was the development of covert bases near to the British base at Gibraltar. The Italians reasoned that to maximize the use of the Maiale it was uneconomic and risky to deploy them from a large transport submarine for every operation. Targets reported by Italian coast watchers in Spain might have moved on by the time the submarine reached the area, and furthermore the operators got `stale' in the passage to the target area. What was wanted was a base on the British doorstep from which they could launch repeated attacks with impunity.
They were fortunate in that the Spanish authorities turned a blind eye to their activities. For Operation BG.3 in May 1941 the Maiale operators went overland to the Italian tanker Fulgor from which they transferred to the submarine. The same modus operandi was used in Operation BG.4 in September 1941. But the Decima Mas planners, and a young Maiale operator TV Licio Visintini, wanted to take this idea one stage further and develop a fully-operational Maiale base overlooking Gibraltar harbour. For this purpose neither the Fulgor nor the Villa Carmela - a house in Algeciras also used by Italian Gamma swimmers to attack shipping at Gibraltar were suitable. The Fulgor lay too far away at Cadiz and, in any case, any attempt to move her nearer to Gibraltar would arouse the suspicion of the British. The Villa Carmela was but could not he used regularly for operations and it would be out of the question to take the Maiale directly to the beach for launching from there. Such a course of action would stretch the patience of the Spanish authorities too far.
Instead Visintini focused on the Italian tanker Olterra lying at Algeciras. She had been scuttled by her Italian crew on the outbreak of war but had been refloated by the Spanish and secured inside the breakwater. A guard consisting of a corporal and four privates of the Guardia Civilia was mounted to prevent all unauthorized personnel boarding the ;hip. In March 1941 members of the Olterra's original crew including Paolo Denegri, the Chief Engineer, returned the ship to act as a care and maintenance party. The Italians were provided with special passes allowing them to board the ship. Visintini arrived onboard Olterra on 27 June 1942 with civilian papers identifying him as Lino Valeri, the prospective First Officer of the Olterra. He brought three technicians with him and also a medical technician. These four men were to become the core of the Olterra’s Decima Mas detachment and would remain on the ship until operations ceased in September 1943. Visintini lust no time in getting to work. Four members of the Olterra’s mercantile crew- were transferred to another ship on the ground, that they were indiscreet. At the same time Visintini banned the Spanish guards from Visiting the forward part of the ship on the grounds that he suspected them of stealing- food. Denegri and the three `technicians' fulfilled a number of roles.
Preparing the Maiale was their most important function together with acting as `dressers' for the operators, but they also under took a number of other tasks including daytime reconnaissance of shipping in Gibraltar (they were often spotted by British agents doing this) by telescope from the ship's bridge and acting as enforcers to keep away any curious Spaniards.
With the unreliable elements of the crew dismissed and the Spanish guard confined to the stern, Visintini briefed those remaining on Olterra’s new role as a base for Maiale operations against Gibraltar. In order to facilitate operations of the Maiale a forward bulkhead was cut and hinged to give access to the forepeak. Torpedo racks were manufactured ashore in Algeciras and assembled in the forepeak. Finally the tanker was trimmed down by the stern to allow the cutting of a hinged trapdoor measuring 5ft x 8ft in the hull. The cutting took about two hours after which the trim was returned to normal so that the opening was hidden below the waterline. The cutting party was hidden by pontoons and stages moored alongside for painting and minor repairs to the ship's hull. Cables for charging batteries were brought from the dynamos at the stern concealed inside water pipes. The Maiale were broken down into their component parts and packed into wooden crates, together with mines, Belloni suits, clamps, oxygen cylinders and all the other equipment needed for Maiale operations, and shipped to Algeciras by road directly from Italy. Some of the crates were labeled as engineering spares and at least one box was filled with boiler tubes and left with one end opened for the benefit of the curious. Other material was collected by Denegri from the Italian Embassy in Madrid where it had been sent by diplomatic courier. On another occasion a member of Olterra's crew was granted compassionate leave to return to Italy. On his return he brought a crate of limpet mines with him. The arrival of such a large amount of equipment officially destined for a derelict tanker did not apparently arouse the slightest suspicion or concern among the Spanish authorities. The use of the Olterra as a covert base for Maiale operations was and remains one of the most audacious stories of the Second World War.
The Regia Marina employed Maiale against British targets at Alexandria and Gibraltar. Space precludes a description of such operations and excellent accounts exist in both English and Italian. The table below gives a list of their successes but does scant justice to the effect these operations had on the British. The Maiale and their operators were rightly respected. In 1943 a young Italian naval officer, Gino Birindelli, who been captured during the Maiale attack on Gibraltar in October 1940, was due to be repatriated to Italy on health grounds. Just as he was about to set foot on the repatriation ship, he was seized by Military Police and put on the next POW transport to Canada. The Admiralty considered that even in his weakened condition he could not be allowed to return to Italy to give others the benefit of his experience.
This is an impressive total under any circumstances but reflecting on these operations, Admiral Gino Birindelli, who had been captured in Operation BG.2, considered that the Italians failed to make the most of this weapon. Decima Mas Maiale attacks were planned to inflict the maximum damage possible but little or no consideration was to given to the wider Axis plan of campaign. Birindelli offers the opinion that the successful GA.3 operation, if combined with a successful land offensive, could have had effects out of all proportion to the scale of the operation. Sadly Italy's lack of economic muscle and shortage of strategic materials did not permit this sort of grandiose planning. Decima Mas had the capacity to be a strategic weapon but ultimately it could never be more than a highly effective irritant. Nevertheless the Italian flair for this sort of underwater warfare had been amply demonstrated.