A system used in wartime to arrange for merchant vessels to sail in groups under the protection of an armed naval escort. In 1917 Germany’s policy of unrestricted submarine (U-boat) warfare nearly defeated Britain. One ship in four leaving British ports was sunk; new construction only replaced one-tenth of lost tonnage. In the face of this crisis Lloyd George overruled the Admiralty’s refusal to organize convoys, and by November 1918, 80% of shipping, including foreign vessels, came in convoy. In World War II transatlantic convoys were immediately instituted in spite of a shortage of destroyers, using long-range aircraft for protection. During 1942 they were extended to the USA as the Allies were losing an average of 96 ships a month.