Italian raid on Pola

On the night of 13/14 May 1918 the Italian navy tried to force its way into Pola (Pula), the main base of the Austro-Hungarian fleet, where the Tegetthoff-class dreadnoughts lay at anchor. A new and unusual weapon was used in the attack: the boat Grillo, which thanks to spiked chains on her sides was meant to clamber over the floating booms guarding the harbour entrance. Grillo got past several lines of booms, but the Austrians spotted and sank her before she could fire her torpedoes. Four members of her crew were taken prisoner.

Since the beginning of the war the Austro-Hungarian fleet had rarely left its heavily fortified bases, and the Italian Regia Marina did not want to risk its battleships in a battle in the narrow Adriatic. Instead it waged a “small war” with fast MAS torpedo boats. After Luigi Rizzo’s boats sank the battleship Wien in the roads of Trieste in December 1917, Pola became the target. Its entrance, however, was closed by several parallel lines of booms made of beams, cables and nets, which an ordinary motor boat could not force.

A solution was proposed by the engineer Attilio Bisio of the SVAN yard in Venice, the designer of the first MAS boats. In the arsenal in Venice four flat-bottomed, sixteen-metre boats were built and named after jumping insects: Cavalletta, Grillo, Locusta and Pulce. They were driven by quiet electric motors, and along both sides ran chains with hooks that resembled the caterpillar tracks of British tanks. The hooks were meant to grip the beams of the boom and haul the boat across to the other side. Each boat had a crew of four and two 450 mm torpedoes. The boats were slow, however, making only a few knots, so they had to be towed close to the target by MAS boats. The first attempts failed: in mid-April Cavalletta and Pulce did not reach the booms before dawn and their crews scuttled them. Several sorties by Grillo at the beginning of May also had to be broken off because of the weather and breakdowns.

On the evening of 13 May two MAS boats, escorted by destroyers, towed Grillo close to Pola. The boat was commanded by Lieutenant Commander Mario Pellegrini, who had taken part in the attack on Trieste in December 1917. Grillo reached the first boom, but the grinding of the chains on the wooden beams alerted the defences. The boat was caught in a searchlight and came under fire, yet she still got across further booms. Sources differ as to how many she passed: according to some three, according to others four out of five. Then an Austrian patrol boat headed towards her. According to Italian accounts the crew still tried to fire the torpedoes blind, but did not have time to arm them. Pellegrini ordered the boat scuttled, and a hit from a gun capsized her. All four sailors were fished out of the water and taken prisoner, one of them seriously wounded.

The Austrians raised the wreck of Grillo and examined it thoroughly, and before the end of the war they had begun building a copy of it. Pellegrini returned from captivity at the end of November 1918 and received Italy’s highest military decoration, the gold Medal of Military Valour. The failed raid showed that Italian sailors had no intention of leaving the Austro-Hungarian fleet in peace even in its best-defended base.