thumb|right|British [[Naval drifter|drifters sailing from their base in the Adriatic to man the Otranto Barrage]]
The Otranto Barrage was an Allied naval blockade of the Strait of Otranto between Brindisi in Italy and Corfu on the Greek side of the Adriatic Sea in the First World War. The operation consisted of over 200 vessels at the height of the blockade. The blockade was intended to prevent the Austro-Hungarian Navy from escaping into the Mediterranean and threatening Allied operations there. The blockade was effective in preventing surface ships from escaping the Adriatic, but it had little or no effect on the submarines based at Cattaro.
Blockade attempt
thumb|right|Location of the Otranto Barrage
The Adriatic is wide at the Otranto Straits. The blockade consisted of over 200 vessels at its height, mainly British and French. A main force of up to 60 drifters were dedicated to anti-submarine operations. The drifters were mostly British and typically armed with a 6-pounder gun and depth charges. In 1915 when the blockade was begun, two divisions of 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. A third division would be at Brindisi. was caught by the indicator nets during the course of the war (other submarines were sunk by mines of the barrage: UB53, and probably UB44 and U30). It was later considered that the straits had simply been too wide to be netted, mined or patrolled effectively. His second-in-command was another British officer, Commander Charles Edward Turle. The largest raid was carried out on the night of 14/15 May 1917 by the cruisers , , and supported by the destroyers and and Austro-Hungarian U-boats and , along with German U-boat (operating as Austro-Hungarian U-boat U-89). The fleet, commanded by Commodore Miklós Horthy, sank 14 drifters out of 47 on duty, and damaged a further three seriously.