Starving the enemy of essential food and raw materials by cutting off their supply lines was, they calculated, a surefire way of bringing their foes to their knees.
It was for this very reason that, in both 1915 and 1917, the Germans declared all-out submarine warfare on commercial shipping heading to Britain. Between February and April 1917, they sank no less than 500 vessels, and in the second half of April were sending 13 ships to the seabed every day. Suddenly Britain found itself with just six weeks’ worth of wheat – and some feared that the country might be starved out of the war.
Yet the tide was soon to turn, thanks to the introduction of convoys – in which Allied vessels travelled in groups, often with protection from warships. This, combined with innovations such as depth charges, meant that, by 1918, the Allies had largely nullified the u-boat threat.