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c h a p t e r t h r e e THE austrians Prepare an attack In the middle of May 1917, the k.u.k. Kriegsmarine risked the most modern and effective of its small force of light cruisers and destroyers on a raid on the drifter line in the Otranto Straits. A glance at a map would easily show that this was indeed a risk, for a raiding force would have to pass south of the parallel of Brindisi, where there were considerable Allied light forces, and would consequently be in the potential position of having an avenging enemy force between it and the safety of its base in the Gulf of Cattaro. That the Austrians were prepared to take this risk would seem to indicate that they considered disruption of the drifter line to be worth it, which leads to the assumption that the work of the drifters was at least annoying enough to provoke the action . What effect then were the drifters having on Austrian and German submarine operations? During the war large numbers of former ¤shing craft were taken over by the Admiralty for naval service. There were two main types, trawlers and drifters. Trawlers and drifters are frequently referred to in the same context, and to the untrained eye they may appear similar in photographs. There are, however, differences between them due to their different functions. Trawlers are larger than drifters and because of their role in trawling the ocean, that is dragging nets, they are equipped with more powerful engines. Consequently they tend to be better suited than drifters for minesweeping. Drifters, as their name implies , work in a more passive manner after shooting their nets. At the Strait of Otranto the drifters operated on a deceptively simple prin- 36 the battle of the otranto straits ciple. They deployed astern wire mesh nets 180 feet deep. This implies a naive notion that the submarine was a giant steel ¤sh to be netted, but that was not the case. The nets were so-called “indicator nets,” that is, they were ¤tted with buoys released by the violent motion of a submarine maneuvering against the nets.1 The buoys, devised to ignite and burn calcium when fouled, would thereby betray the presence of a submarine under the surface. The alarm would be given and, if suitably armed, the drifter might drop depth charges. The submarine would have lost a large measure of its greatest asset, its invisibility. There might be an added dividend. Should the nets become entangled in the submarine ’s screws, the ability of the submarine to maneuver or escape might be limited. Submarine commanders would be aware of this nightmarish possibility and the drifters might therefore have a deterrent value, or perhaps might channel submarines toward mine¤elds.2 The French and Italians had proposed a ¤xed mine-net barrage in the Otranto Straits. This would have been a wire net ¤tted with mines supported by mooring buoys. The objective was for any submarine coming in contact with the net to detonate one of the mines. This was potentially more destructive , although as we have seen in the preceding chapter the Admiralty had reservations about the feasibility of the French and Italian schemes, particularly how such a net could be maintained or the mines serviced or inspected to see if they were still functioning. By the spring of 1917, indicator nets had achieved little in the way of success in terms of submarines actually destroyed.3 The drifters had been at work more than seven months before they caught a submarine, and that success was to a certain extent accidental. The Austrian submarine U.6 under the command of Linienschiffsleutnant Hugo von Falkhausen left the Bocche on the evening of 12 May 1916 to seek enemy traf¤c along the line from Cape Santa Maria di Leuca to Valona. The submarine was a 240-ton Holland type boat built at the Whitehead Yard in Fiume and placed in service in the summer of 1910.4 The following night, the 13th, in the middle of the Otranto Straits, Falkhausen spotted a drifter a few hundred meters ahead. He promptly submerged and turned toward the east only to spot a second drifter steering parallel to the ¤rst twenty minutes later. He decided to break through the approximately 500meter gap that he perceived between the drifters at a depth of thirty meters. A short while later there was an unexplained noise of something on...

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