28 December ended in failure caused by operating problems due to the extreme cold, and one of the airships was destroyed in a forced landing at Seerappen. The plan was subsequently abandoned. In 1917 the German High Command made an attempt to use a Zeppelin to deliver supplies to Lettow-Vorbeck's forces in German East Africa. L 57, a specially lengthened craft was to have flown the mission but was destroyed shortly after completion. A Zeppelin then under construction, L 59, was then modified for the mission: it set off from Yambol on 21 November 1917 and nearly reached its destination, but was ordered to return by radio. Its journey covered and lasted 95 hours. It was then used for reconnaissance and bombing missions in the eastern Mediterranean. It flew one bombing mission against Naples on 10–11 March 1918. A planned attack on Suez was turned back by high winds, and on 7 April 1918 it was on a mission to bomb the British naval base at Malta when it caught fire over the Straits of Otranto, with the loss of all its crew. On 5 January 1918, a fire at Ahlhorn destroyed four of the specialised double sheds along with four Zeppelins and one Schütte-Lanz. In July 1918, the Tondern raid conducted by the RAF and Royal Navy, destroyed two Zeppelins in their sheds. 1914–1918 naval patrols The main use of the airship was in reconnaissance over the North Sea and the Baltic, and the majority of airships manufactured were used by the Navy. Patrolling had priority over any other airship activity. During the war almost 1,000 missions were flown over the North Sea alone, compared with about 50 strategic bombing raids. The German Navy had some 15 Zeppelins in commission by the end of 1915 and was able to have two or more patrolling continuously at any one time. However their operations were limited by weather conditions. On 16 February, L 3 and L 4 were lost owing to a combination of engine failure and high winds, L 3 crashing on the Danish island of Fanø without loss of life and L 4 coming down at Blaavands Huk; eleven crew escaped from the forward gondola, after which the lightened airship with four crew members remaining in the aft engine car was blown out to sea and lost. At this stage in the war there was no clear doctrine for