Otranto Barrage - Blockade Attempt

Blockade Attempt

The Adriatic is 100 km (54 nmi; 62 mi) wide at the Otranto Straits. The blockade consisted mainly of a fleet of drifters, most of them British, and usually armed with a 6-pounder gun and depth charges. 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 drifters were supported by destroyers and aircraft. However, the demands of the Gallipoli Campaign and other naval operations left the Otranto Barrage with insufficient resources to deter the U-boats, and only the Austro-Hungarian U-6 was caught by the indicator nets during the course of the war. It was later considered that the straits had simply been too wide to be netted, mined or patrolled effectively.

The ease with which German and Austrian submarines continued out of the Austro-Hungarian ports in spite of the barrage (and the success they had in disrupting shipping in the whole of the Mediterranean) strongly embarrassed the Allies, the system being called "a large sieve through which U-boats could pass with impunity". In 1917–1918, reinforcements from the Australian and American navies brought the blockading force up to 35 destroyers, 52 drifters and more than 100 other vessels. But submarines continued to slip through until the end of the war, while only the introduction of the convoy system and better coordination amongst the Allies helped to cut the losses they were causing.