Otranto Barrage

[2][3] 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.

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[5] was caught by the indicator nets during the course of the war.

[3] 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".

[citation needed] Nevertheless, submarines continued to slip through until the end of the war; the introduction of the convoy system and better coordination amongst the Allies only helped to cut the losses they were causing after escaping the blockade.

[3] By contrast, the presence of Allied capital ships involved in the blockade was generally successful in its mission of keeping enemy surface vessels from leaving the Adriatic Sea.

However, the British cruisers broke off the engagement when the Italian flag officer received notice of heavy Austrian forces coming out of Cattaro.