Austro-Hungarian seaplanes L.132 and L.135 forced the French submarine to surface by dropping bombs. L.135 finally sinks the sub while the 27 survivors were clinging to the two planes now floating, to be finally saved by the alarmed Tb 100M. This was the first sinking of a submarine by airplanes in naval war history. The very same day, the French submarine Ampére scored two torpedo hits on the Austro-Hungarian Hospital ship No I (the former Lloyd steamer Elektra) off Cape Planka (Rt Ploča), causing two fatalities. The damaged hospital ship had to be beached in Borovica Bay for further repairs. On the night of 22/23 December, the Austro-Hungarian destroyers , , and Velebit attacked the drifters patrolling the Otranto barrage, which applied for help to the French destroyers , , , , and which were escorting a convoy from Brindisi to Taranto. Because of communication problems, only Casque and Commandant Rivière attacked, but Casques boiler rooms were hit immediately and she had to slow down to . For further assistance, the Italian destroyers , and left Brindisi shortly followed by the British cruiser Gloucester escorted by and . The French and Italian groups met during darkness, Giuseppe Cesare Abba rammed Casque; some moments later, Boutefeu rammed Giuseppe Cesare Abba. While the damaged vessels had to be taken into tow, the Austrians escaped in the darkness. The return from the Otranto battle—15 May 1917—brought the British cruiser within the range of the which had already laid mines off Brindisi. At 13:30, UC-25 torpedoed Dartmouth approximately off Brindisi, for some time the ship was considered to be lost, but was manned by a rescue crew later and finally towed into port. On hearing that Dartmouth had been torpedoed, Boutefeu went to assist, only to hit one of UC-25s mines. 1917 The Austro-Hungarian Navy had a major victory in May 1917 when it broke out of the allied naval blocked of the Adriatic Sea during the Battle of the Strait of Otranto (1917), however after this, large scale operations were limited. By August 1917, Lt. Von Trapp and U-14 had sunk more than of enemy shipping, including the Italian steamer Milazzo (). U-4 torpedoed the French steamer Italia near Taranto on 30 May, and on 16 November severely damaged the Italian steamer Oriona between Brindisi and Valona. On the night of 9–10 December, while SMS Wien and Budapest were at anchor in Trieste,