Convoys in World War I
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.
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.
Losses to enemy submarines were drastically cut from the level of the previous year,[1] and only five freighters were lost before the war's end.
[5] 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.
[1] When shippers from Norway (the "neutral ally") requested convoys in 1916 after a year of very serious losses, but refused to accept the routes chosen by the Admiralty, they were declined.
It was not until 860,334 long tons (874,140 t) of shipping were lost to U-boats in April (and British Isles grain reserves had dropped to a six-week supply)[6] that the Admiralty approved convoying all shipments coming through the north and south Atlantic.
[1] The first experimental convoy of merchant vessels left Gibraltar on 10 May 1917 and arrived at the Downs on 22 May,[1] having been accompanied by the last leg of its journey by a flying boat from the Scillies.
[6] Confidence in the convoy system grew rapidly in the summer of 1917, especially as it was realised that the ratio of merchant vessels to warship could be higher than previously thought.
Shortly after the U.S. entered the war, Sims brought over 30 destroyers to the waters around Britain to make up the Royal Navy's deficit.
[1] The Germans again responded by changing strategy and concentrating on the Mediterranean theater, where the extremely limited use of convoys had been approved at the Corfu Conference (28 April–1 May 1916).
[9] The commander-in-chief of the Royal Navy in the Mediterranean, Somerset Calthorpe, began introducing the convoy system for the route from Port Said to Britain in mid-October 1917.
[1] Calthorpe remained short of escorts and was unable to cover all Mediterranean trade, but his request to divert warships from convoy duty to the less effective Otranto Barrage was denied by the Admiralty.
It alleged that convoys presented larger and easier targets to U-boats, and harder object to defend by the Navy, raising the danger of the submarine threat rather than lowering it.
It cited the difficulty of coordinating a rendezvous, which would lead to vulnerability while the merchant ships were in the process of assembling, and a greater risk of mines.
The Admiralty also showed a distrust of the merchant skippers: they could not manoeuvre in company, especially considering that the ships would have various top speeds, nor could they be expected to keep station.
Finally, the Admiralty suggested that a large number of merchantmen arriving simultaneously would be too much tonnage for the ports to handle, but this, too, was based in part on the miscalculation.
In fact, it reduced the number of available targets for U-boats, forcing them to attack well-defended positions and usually giving them only a single chance, since the escorting warships would respond with a counterattack.
It also "narrowed to the least possible limits [the area in which the submarine is to be hunted]", according to the Anti-Submarine Report of the Royal Navy Air Service (RNAS) of December 1917.
[3] The fourth category is the "coastal convoys", those protecting trade and ship movements along the coast of Britain and within British home waters.
[3] The Enemy Submarine and Direction Finding Section and the code-breakers of Room 40 cooperated to give the convoy planners knowledge of U-boat movements.
In July, the Antisubmarine Division and the Air Department of the Admiralty considered and rejected the use of searchlights during night, believing the airships would render themselves vulnerable to surfaced U-boats.
[6] On 26 December 1917, as an airship was escorting three merchantmen out of Falmouth for their rendezvous with a convoy, they were attacked three times in the space of 90 minutes, torpedoing and sinking two of the vessels and narrowly missing the third before escaping.
The northeast of England led the way in the use of aircraft for short- and long-range escort duty, but shore-based aerial "hunting patrols" were widely considered a superior use of air resources.
