By Dr Eric Grove
Last updated 2011-02-17
The U-boat threat The Germans were slower than the British in adopting submarines but, as the inferior naval power on the surface, they had more scope for using them to neutralise British command of the sea by attacking both warships and merchant ships. German submarines, or U-boats (Unterseebooten), were turned against merchant ships supplying Britain in February 1915. This was after some successes against warships, and was in retaliation for the increasingly tight British blockade preventing ships carrying vital supplies from reaching Germany.
Submarines could not operate by the conventional rules of merchant raiding, and sometimes they torpedoed on sight. The U-boats' most notable victim was the liner Lusitania, sunk by U-20 on 7 May; this caused the loss of 1,201 lives, with 128 Americans among them. Subsequent American complaints led to orders not to sink liners, but on 19 August U-27 sank the Arabic, killing more Americans. Pressure from Washington now forced the Germans to give up these attacks.
In October 1916, the U-boats began another campaign against commerce. At first they operated under various restrictions, but these were withdrawn on 1 February 1917. American outrage caused the US to enter the war on 6 April. That month, Allied shipping losses were over 860,000 tons. This was unsustainable, and the Allies found they could solve the problem by putting merchant ships into defended convoys. The system was introduced slowly, and proved very successful - and although many ships still sailed independently, those in convoys were safe. Monthly losses were halved by the end of the year. The U-boats had been neutralised.
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