While the Japanese navy was planning its attack on Pearl Harbour the Royal Navy prepared to launch a very similar operation. On the night of 11/12 November 1940, 21 Fairey Swordfish torpedo-bomber biplanes of the Fleet Air Arm struck at the Italian fleet in Taranto harbour and, in the first major and successful strike by naval aircraft, effectively redressed the balance of sea power in the Mediterranean in British favour. Italy's entry into the war in June 1940 and the subsequent elimination of the French fleet had given the Axis superiority at sea in the Mediterranean, a situation that seriously threatened British convoys sailing to the UK with vital supplies from the dominions east of Suez. Moreover, following Italy's attack on Greece in October that year, undisputed use of the Aegean and Adriatic by the Axis powers posed considerable difficulties in the support of any British foothold in the Balkans that might be considered. Three of the 'Zara' class cruisers were lying in the centre of the Mar Grande when the Swordfish made their attack. In addition to their main armament each carried 16 dual-purpose 100mm (3.92in) guns, a powerful anti-aircraft battery in itself. Key to any operations in the central Mediterranean by the Royal Navy lay in the continued use of Malta, both as a naval and air base, and it was with a fine sense of history that it had been intended to bring the Italian fleet to battle on 21 October (Trafalgar Day) with a British fleet of four battleships and battle-cruisers, two carriers (HMS Eagle and Illustrious), 10 cruisers and four destroyer flotillas. Despite the sailing of two convoys through the Mediterranean, the Italian fleet (comprising five battleships, 14 cruisers and 27 destroyers) declined to leave its base at Taranto; moreover, following a number of near misses from Italian bombers, the carrier Eagle was suffering mechanical troubles, necessitating the transfer of her Swordfish aircraft to the Illustrious. Vittorio Veneto was not hit during the Taranto raid but her sister ship Littorio suffered three torpedo hits leaving her under repair until Apri/1941. Capable of 30 knots and armed with high velocity 381mm (15in) guns, these magnificent battleships seriously threatened the British position in the Mediterranean. The Italian air force failed to detect the approach of the British fleet to within range of Taranto. A few lumbering flying boats came near, but were shot down by British Fulmar fighters operating under radar control. So the raid achieved complete surprise and sank half the Italian navy's battleships, altering the balance of power in the Mediterranean at a stroke. The British were lucky: after storms earlier in the week only 27 of the 90 barrage balloons protecting the ships were still in the air on the night of the attack, and the Italian torpedo nets did not extend deep enough to protect the ships properly.