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“Viribius Unitis” An Austro- Hungarian battleship sunk by frogmen during WW1. Old Postcard, unknown source. During the first years of in their harbours, sur- World War II Italian rounded by mine-fields and anti-submarine frogmen demon- nets. This passivity was, strated to the world in the main, due to the how effective a ongoing submarine war. weapon a frogman In 1915, after Italy had severed its connec- could be. Hidden tions with its German and by the water, these Austrian allies, and joined frogmen mined the the English-French Alliance, Allies’ ships as they Italian naval officers had thought long and hard about were moored ‘safely’ how the Austro-Hungarian fleet in their own waters. could be attacked in the harbour. TBy Sven Erikh Jørgensene - The DanishF Society ofi Divingr Historys t Frogmen Even with quite small numbers, and using The first attempt, carried out from Viribus Unitis siinking after relatively small resources, the frogmen were Venice, was made by the Italian naval being mined by divers a very powerful force. The English, especially, captain Pellegrine, who, with three other were quick to copy the equipment and train crew members in a motor-boat, tried to their own frogmen, and after the war many attack the Austro-Hungarian fleet in Pola. nations supplemented their armed forces with Pellegine’s boat Grillo was equipped frogmen units. with caterpillar tracks which enabled it The idea of such a weapon arose in World to crawl up over the various barriers in War I, when experiments were carried out us- Pola. Two torpedoes, which hung on the ing different vessels to carry mines into the Aus- side of the boat, were to be sent against tro-Hungarian naval base in Pola. The weapon the ships in the harbour. Pellegrine’s was developed during the inter-war years attempt failed because the boat was discovered as it was forc- 1915 ing a barrier. While the war was raging on the battlefields Pellegrine and his of Europe, and submarines were terrorising the crew spent the ships on the high seas, the Austro-Hungarian rest of the war in fleet and Italian fleet lay mostly well protected captivity. Two attack divers astride a SLC - Siluro a Lenta Corsa (slowlly moving torpedo) 67 X-RAY MAG : 7 : 2005 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Naval-lieutenant Raffaele Paolucci Pola, or Pula, lies at the tip of the peninsula of Istria, now in Croatia, at the top of the Adriatic sea 1918 whereby he was to be transported by motorboat to about a sea-mile out of Pola. From here he would swim into the harbour towing a mine. Under one of the battleships he would tie a four meter-long Pellegine’s boat Grillo was equipped with caterpillar tracks which ena- rope to the mine and thereaf- bled it to crawl up over the various barriers in Pola ter sink it by letting the air out of its two floatation tanks. The Mignatta, a other end of the rope was to compressed Captain Constanzo Mignatta close in to Pola. At 22.13 the S2 be fixed to the hull of the ship. air minisub Ciano had been was released from the motorboat and The mine, which contained for carrying watching the efforts sailed in to Pola, which was reached at about 100 kg of TNT, had an divers of the two men, and 02.00 on 1 November, 1918. In the har- automatic timer, and would asked them to cooper- bour the two men passed three anti-sub- explode in about 4 meters of ate with him in com- marine nets by pulling the S2 over them. water close to the side of the pleting the project with Once inside the harbour they steered ship. As soon as the mine was Mignatta. This coop- in between two illuminated battleships activated Paolucci would eration soon proved to and directly towards the 21000 ton bat- swim out of the harbour towards the be effective, and after tleship Viribus Unitis. They fixed one of Targetting Pola outer breakwater and wait for the explo- several tests and modi- the mines and then rapidly sailed away The desire to hit the Austro-Hungarian sion. He would then swim out to sea and, fications Mignatta was – leaving a trail of silvery bubbles. fleet in Pola was, however, undimin- with his back to the enemy, signal to the pressed-air torpedo, named Mignatta, ready for action. Two models of Mignatta On their course away from the battle- ished, and much thought was put into motorboat to pick him up. which, half-submerged, would carry him were built, S1 and S2. ship they were discovered, but before possible solutions. Naval-lieutenant and another crew member into Pola. The being taken prisoner they had managed Raffaele Paolucci worked out a plan in Mignatta men, in diving suits, would sit astride the Now or never to arm the second mine, and then left After months of nocturnal swimming near torpedo and steer it into the harbour and However, in October 1918, an armistice the Mignatta to its own devices. It wan- Venice, towing a mock-up of the mine, thereafter over to one of the battleships. was in the offing, and it was obvious dered around in the harbour, and when Limpret mine being fixed to he abandoned the project. Two mines, each of 170 kg TNT, were that it was now or never if the Mignatta the compressed-air was exhausted it the bottom of a vessel Simultaneously with fixed to the head of the torpedo. The was to see action. In the evening of 31 finally came to rest against one of the the efforts of Paolucci, mines were to be hung in a 4 meter-long October, 1918, a motortorpedo boat ships. Italian engineer and rope under one of the battleships. Rosetti from Venice set sail for Pola. On board naval officer Raffaele had constructed a powerful magnet were Paolucci and Rossetti and, on the War’s over - well almost Rossetti was working which should keep the rope fixed to the deck, the S2 and a motorboat which That they were not discovered before on a modified com- side of the ship. would carry the two men and the was due to the fact that it was a day Sideview of the Mignatta 68 X-RAY MAG : 7: 2005 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Italian naval officer Teseo Tesei was one of the developers of feature Dive History a new branch of underwater weapon thought to be no reason to keep the The First Frogmen Further developments watertight doors closed. Immediately It was two Italian divers and naval offic- Teschi and Tesei served as after this first explosion a second explo- ers, Teseo Tesei and Elios Toschi, inspired engineers for the subma- sion was heard. It was the second mine, by Rossetti’s Mignatta, who would rines at the naval base at La still attached to the Mignatta, that begin the development of the weapon Specia. The development and exploded directly against the side of the that the world would come to know as construction of an improved 7000 ton freighter Wien, and sent her to “Frogmen”. However, before this weap- Mignetta started in 1935, and in the bottom. Ten days after Viribus Unitis on could be brought into service, diving January two prototypes were had been sunk Germany accepted the suits, breathing apparata and ‘torpe- tested. Later in the year the Armistice conditions, and World War I does’ had to be developed. new weapon was demonstrat- was brought to a close. ed, under the strictest secrecy, for the Admiralty in a dock at New weaponry Divers preparing a limpet the La Spezia basin. The attack at Pola was a suc- mine before a mission cess – the Italian fleet had The Maiale obtained insight into a new The weapon mostly resembled weapon. The weaknesses of a torpedo but was in fact a mini- the weapon were that the ature submarine designated SLC (Siluro a which permitted the crew to increase crew were visible above the Lenta Corsa) with the nickname Maiale or decrease the buoyancy. A separate surface of the water, and (the pig). The torpedo was 7.3 m long, compartment contained compressed-air that the compressed-air tor- including the explosive head, the diam- tools to cut through a submarine net. A pedo sent out a stream of air- eter was 0.53 m, and two frogmen could screen in front of the leading frogman bubbles. These deficiencies sit astride it. The compressed-air motor protected the crew against the water would have to be corrected had been replaced by a 1.1 HP electric flow. Behing the screen were the steer- so that an attack could be motor. The power of the motor was later ing controls and the luminous navigation carried out with the torpedo increased to 1.6 HP. In 1935 the explosive equipment. The maximum diving depth and crew completely sub- weighed 220 kg, but was later increased was 40 meters. merged, and without air-bub- to 250 kg and thereafter to two amounts The crew wore waterproof Belloni suits bles giving evidence of the of explosive, each of 150 kg. The capac- (Vestito Belloni) constructed by Captain attack. ity of the batteries allowed a voyage of Belloni. The Belloni suit actually consisted 5 seamiles at 2.3 knots or 4 seamiles at of two suits, an inner suit of thin elastic The interwar years 4.5 knots.