The convoy—a group of merchantmen or troopships traveling together with a naval escort—was revived during World War I (1914–18), after having been discarded at the start of the Age of Steam. Although convoys were used by the Royal Navy in 1914 to escort troopships from the Dominions, and in 1915 by both it and the French Navy to cover their own troop movements for overseas service, they were not systematically employed by any belligerent navy until 1916. The Royal Navy was the major user and developer of the modern convoy system, and regular transoceanic convoying began in June 1917. They made heavy use of aircraft for escorts, especially in coastal waters, an obvious departure from the convoy practices of the Age of Sail.
As historian Paul E. Fontenoy put it, "[t]he convoy system defeated the German submarine campaign." From June 1917 on, the Germans were unable to meet their set objective of sinking of enemy shipping per month. In 1918, they were rarely able to sink more than . Between May 1917 and the end of the war on 11 November 1918, only 154 of 16,539 vessels convoyed across the Atlantic had been sunk, of which 16 were lost through the natural perils of sea travel and a further 36 because they were stragglers.
Development
Origins
The first large convoy of the war was the Australian and New Zealand Army Corps (ANZAC) convoy. On 18 October 1914, the Japanese battlecruiser left the port of Wellington, New Zealand, with 10 troopships. They joined 28 Australian ships and the Australian light cruisers and Melbourne at Albany, Western Australia. The Japanese also sent the cruiser to patrol the Indian Ocean during the convoy's crossing to Aden. During the crossing, HMAS Sydney was caught up in the Battle of Cocos (9 November), but the Japanese-escorted convoy reached Aden on 25 November. The Japanese continued to escort ANZAC convoys throughout the war. The convoys of Dominion troops were, weather permitting, escorted into port by airships.
With the advent of commerce raiding by the submarines of the Royal Navy, the Imperial Russian Navy, and the Kaiserliche Marine (Imperial German Navy), it was neutral Sweden, at the insistence of Germany, that first used a convoy system in early November 1915 to protect its own merchant shipping after the British and the Russians attacked its iron ore shipments to Germany. The German merchant fleet proposed a similar expedient, but the navy refused. However, in April 1916, Admiral Prince Heinrich of Prussia—commander-in-chief in the Baltic theater—approved regular scheduled escorts for German ships to Sweden. Losses to enemy submarines were drastically cut from the level of the previous year, and only five freighters were lost before the war's end. In June 1916, the Baltic Fleet attacked a German convoy in the Bråviken, destroying the Q-ship Schiff H and some Swedish merchantmen, before mistakes by the commander of the Destroyer Division—Aleksandr Vasiliyevich Kolchak—allowed the majority of the convoy to escape back to Norrköping.
Revival
To cover trade with the neutral Netherlands, the British instituted their first regular convoy on 26 July 1916, from the Hook of Holland to Harwich, a route targeted by the German U-boats based out of Flanders. Only one straggler was lost before the Germans announced unrestricted submarine warfare on 1 February 1917, and only six after that before the war's end despite 1,861 sailings. The Holland convoys were sometimes referred to as the "Beef Trip" on account of the large proportion of food transported. They were escorted by destroyers of the Harwich Force and, later in the war, by AD Flying Boats based out of Felixstowe.