In the aftermath of Rizzo's attack on Wien, the Austrians strengthened their boom defenses until hand-held hydraulic shears could no longer overcome them. The Italians responded with a special type of MAS, the Grillo or "Cricket." This was a slow, quiet, electrically driven boat inspired by the British rhomboid tanks. It combined the flat-bottomed hull of a landing craft with a pair of 45-cm torpedoes in side-dropping gear and two hook-studded, engine-driven chains mounted on either side of the hull. The Grillo could approach boom defenses quietly and clamber over them, much like a tank crushing barbed wire. Once inside the anchorage, it would attack with its torpedoes and retire the way it came. The Grillo was not very successful in action. The chain mechanism produced a frightful clatter that all but negated the advantage of the silent, 15-hp electric motor. They were usually destroyed by shellfire before they got over the booms. Nevertheless, the Austrian navy was interested enough to raise and copy a sunken example.
Although the Italian Navy started to test its first motor torpedo boats as early as 1906, it was only after Italy's entry into World War I in May 1915 that development progressed. The first craft was commissioned in April 1915, and was soon in production by the Venetian firm SVAN (Societa Veneziana Automobili Navali), so was named Motobarca Armata SVAN, `SVAN armed motorboat'. Following mass production by Isotta Fraschini and FIAT as well, it was renamed Motoscafo Armato Silurante, `armed torpedo motorboat', or MAS. (This acronym was also used for Motoscafo Anti Sommergibile, `anti-submarine motorboat', in which role these craft were sometimes used.) The concept of a motor torpedo boat not only introduced a major change to Italian naval doctrine, but also led to development of other special craft. These included the tracked light assault boat, specifically designed to climb over protection nets; and the `mignatta' (`leech'), subsequently developed into the Torpedine Semovente Rossetti or `Rossetti self-propelled torpedo' - the first attempt to modify a standard torpedo for manned use.
During World War I the Italian Navy mostly fought against the Austro-Hungarian Navy in the narrow waters of the Adriatic Sea. Both sides tried to avoid any fleet engagement that might have cost them irreplaceable major warships, and this led to the development of craft and tactics for `small warfare', with the aim of causing as much damage as possible while putting at risk only light and easily replaceable craft. For Italy, this effort was quite successful. By 1918 some 419 MAS had been produced, 244 of them operational; their most significant successes were the sinking of the Austro-Hungarian battleship Wien on 9 December 1917, and of the dreadnought Szent Istvan on 10 June 1918. But the real step forward was the employment of assault craft, which brought a new dimension to naval warfare. On 13 May 1918 the tracked assault boat Grillo (`Cricket') tried to penetrate the Austro-Hungarian naval base of Pola on the Istrian peninsula (today's Pula, Croatia), and though it ultimately failed it did overcome four of the first five obstacles it encountered.
Italy had now been at war for several years and needed a way of successfully attacking the Austrian main naval base at Pola, another craft had been developed by the Italians called the Grillo which was a fast boat armed with a torpedo, attached to its sides were tracks with hooks so it could haul itself over the tops of booms and torpedo nets. Its first attack was against the ships inside the defended harbour at Pola on the 13th May 1918 but it was a complete disaster, with the craft being put out of action and the crew being taken prisoner.
Another notable mission - although carried out at the time of the Austro-Hungarian surrender, after the fleet had been handed over to the future Yugoslavia - was the sinking of the battleship Viribus Unitis in Pola harbour on 1 November 1918 by a manned torpedo. (This did not really navigate underwater, but was manoeuvred under the bow of the battleship by swimming frogmen.)
By October it was decided it was time for Rossetti and Paolucci to try the craft, so on the night of 31st October 1918 with the Mignatta being carried on the deck of a torpedo boat and escorted by another boat, they left Venice and headed for Pola. When they were off the coast the Mignatta was lowered into the water and towed by the other boat until they were in reach of Pola harbour, they were on their own, it was now 2 am on 1st November. They entered the harbour after climbing over three sets of torpedo nets and pulling the Mignatta over the tops behind them.
Now inside the harbour they made for the Austrian Flagship Viribus Unitis, still undetected they approached the starboard side of the flagship, as they did the Mignatta started to malfunction, the flooding valve on its stern had opened causing it to lose buoyancy and sink. To prevent this the compressed air used to propel the craft had to be used to correct its buoyancy this now meant it had insufficient compressed air to escape from the harbour after the attack.
Regardless of this they carried on with the attack, Rossetti released one of the charges and attached it to the side of the flagship and set the delay fuse for two hours and returned to the Mignatta. Paolucci now headed at full speed towards the shore hoping to try and escape overland, by now it was 5 am. They were spotted by the crew on watch and were illuminated by searchlights, as a motor launch approached them Rossetti quickly set the delay fuse on the last charge and pushed the Mignatta away into the darkness on a slow speed. Rossetti and Paolucci were pulled from the water and taken on board the flagship to be questioned.
At 6.20 am the charge exploded, the flagship immediately listed 20 degrees to starboard, the crew started to abandon ship taking the two prisoners with them, 15 minutes later the 21, 000 ton battleship rolled over and sank. The Mignatta meanwhile had circled the harbour until the air ran out and had settled on the bottom under the hull of the liner Wien, which was being used as a submarine depot ship, the charge exploded sinking the ship.
The two Italians were not prisoners for long as on the 5'h November the Italians occupied Pola, after the armistice both were awarded medals of honour for their bravery and for the building of such a successful new weapon .