Otranto Barrage
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In World War I, the Otranto Barrage was an Allied naval blockade of the Otranto Straits between Brindisi in Italy and Corfu on the Albanian side of the Adriatic Sea. The blockade was intended to prevent the Austro-Hungarian navy from escaping into the Mediterranean and threatening Allied operations there. The blockade, or rather the fleet capital ships in support of it, was effective in preventing surface ships from escaping the Adriatic, but it had little or no effect on the submarines based at Cattaro.
The Adriatic is 100 km (62 miles) wide at the Otranto Straits. The blockade consisted of a fleet of trawlers — in 1915 when the blockade was begun, perhaps 20 would be on patrol at a time — equipped with steel "indicator nets" intended to trap submarines or at least alert the surface vessels to their presence. The trawlers were supported by destroyers and aircraft. However, the demands of the Gallipoli Campaign and other naval operations left the Ontranto Barrage with insufficient resources to deter the U-boats, and from 1915 to 1917 only one, U-6, was caught by the indicator nets.
The Austrians mounted a number of nighttime raids against the barrage, five in 1915, nine in 1916 and ten in 1917. The largest raid was on the night of 14 May–15 May 1917 when the cruisers Novara, Helgoland, and Saida supported by the destroyers Csepel, Balaton and three U-boats, commanded by Admiral Miklós Horthy sank 14 trawlers. The British cruisers Dartmouth and Bristol, together with Italian and French destroyers, under command of Italian Rear Admiral Alfredo Acton steamed from Brindisi to engage the Austrians, resulting in the Battle of the Otranto Straits. The British damaged Saida and disabled Novara, severely injuring Horthy. However, the British cruisers broke off the engagement when the Italian flag officer had notice of heavy Austrian forces coming out of Cattaro and Saida towed Novara back to port. Dartmouth was damaged by a U-boat as it returned to Brindisi. The night before the same U-boat has laid a minefield at the mouth of Brindisi harbour; the French destroyer Boutefeu struck one of these mines exiting the harbour the very same day and exploded, sinking with all hands.
In June 1918 Horthy, by now commander-in-chief of the Austro-Hungarian navy, determined to launch an attack on the barrage employing the four Tegetthoff class battleships based at Pola, the most modern in the fleet. While en route down the Adriatic, the dreadnought Szent István was torpedoed and sunk by an Italian torpedo boat at dawn on 10 June, resulting in the attack being cancelled.
In 1917 and 1918 reinforcements from the Australian and American navies brought the blockading force up to 35 destroyers, 52 trawlers and more than a hundred other vessels. But submarines continued to slip through until the end of the war.
