Convoys in World War I The convoy — a group of merchantmen or troopship s travelling 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 . It was met by 28 Australian ships and the Australian light cruiser . 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 submarine s 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 an auxiliary cruiser 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 destroyer s of the Harwich Force and , later in the war , by AD Flying Boat s based out of Felixstowe . The first convoys to sail after the German announcement were requested by the French Navy , desirous of defending British coal shipments . The Royal Navy ' s first coal convoy crossed the Channel on 10 February . These convoys were more weakly escorted , and contained a mixture of both steam - powered ships and sailing ships , as well as escorting aircraft based on the coast . In all , only 53 ships were lost in 39 , 352 sailings . 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 . After the German proclamation , the Norwegians accepted British demands and informal convoying began in late January or February 1917 , but regular convoys did not begin until 29 April . That same day , the first coastal convoy left Lerwick in the Shetland Islands , the destination of the Norwegian convoys , for the Humber . This was to become a regular route . The Norwegian and coastal convoys included airships based out of Scotland ( and in the latter case also Yorkshire ) . Although the British War Cabinet proposed convoys in March 1917 , the Admiralty still refused . It was not until of shipping were lost to U - boats in April that the Admiralty approved convoying all shipments coming through the north and south Atlantic . Rear Admiral Alexander Duff , head of the Antisubmarine Division , suggested it on 26 April , and the First Sea Lord , Admiral John Jellicoe , approved it the next day . Escorts were to be composed of obsolete cruiser s , armed merchant cruiser s and pre - dreadnought battleship s for the oceanic portion of the routes , while in the more dangerous waters around Britain they were composed of destroyers . Observation balloon s , especially kytoon s , were used to help spot submarines beneath the surface , the aircraft carrier not then being developed . During discussions in March , it was determined that 75 destroyers were needed , but only 43 were available . The first experimental convoy of merchant vessels left Gibraltar on 10 May 1917 and arrived at the Downs on 22 May , having been accompanied by the last leg of its journey by a flying boat from the Scillies . Maturation . The first transatlantic convoy left Hampton Roads on 24 May escorted by the armored cruiser , met up with eight destroyers from Devonport on 6 June , and brought all its ships save one straggler that was torpedoed , into their respective ports by 10 June . The first regular convoy left Hampton Roads on 15 June , the next left Sydney , Nova Scotia on 22 June , and another left New York for the first time on 6 July . The Sydney convoy had to be diverted to Halifax during winter months . The first regular convoy from the south Atlantic commenced on 31 July . Fast convoys embarked from Sierra Leone — a British protectorate — while slow ones left from Dakar in French West Africa . Gibraltar convoys became regular starting on 26 July . 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 . While the first convoys comprised 12 ships , by June they contained 20 , which was increased to 26 in September and 36 in October . The U . S . Navy ′ s liaison to Britain — Rear Admiral William Sims — and its ambassador — Walter H . Page — were both strong supporters of convoying and opponents of Germany ′ s unrestricted submarine warfare . 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 . The success of the convoys forced the German U - boats in the Atlantic to divert their attention from inbound shipping to outbound . In response , the first outbound convoy left for Hampton Roads on 11 August 1917 . It was followed by matching outbound convoys for each regular route . These were escorted by destroyers as they left Britain and were taken over by the typical cruiser fotillas as they entered the open ocean . 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 ) . The Mediterranean proved a more difficult zone for convoying than the Atlantic , because its routes were more complex and the entire sea was considered a danger zone ( like British home waters ) . There the escorts were not provided only by Britain . The French Navy , U . S . Navy , Imperial Japanese Navy , " Regia Marina " ( Royal Italian Navy ) and Brazilian Navy all contributed . The first routes to receive convoy protection were the coal route from Egypt to Italy via Bizerte , French Tunisia , and that between southern metropolitan France and French Algeria . The U . S . took responsibility for the ingoing routes to Gibraltar , and increasingly for most of the eastern Mediterranean . 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 . 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 . With the gradual success of the Mediterranean convoys , the Germans began to concentrate on attacking shipping in Britain ' s coastal waters , as convoyed vessels dispersed to their individual ports . Coastal convoy routes were only added gradually due to the limited availability of escorts , but by the end of the war almost all sea traffic in the war zones was convoyed . The coastal convoys relied heavily on air support . After June 1918 , almost all convoys were escorted in part by land - based airplanes and airships , as well as sea plane s . The organisation of these convoys had also been delegated by the Admiralty to local commanders . Admiralty resistance and objections . The main objection of the Admiralty to providing escorts for merchant shipping ( as opposed to troop transits ) was that it did not have sufficient forces . In large part , this was based on miscalculation . The Admiralty ' s estimates of the number of vessels requiring escort and the number of escorts required per convoy — it mastakenly assumed a 1 : 1 ratio between escorts and merchant vessels — were both wrong . The former error was exposed by Commander R . G . H . Henderson of the Antisubmarine Division and Norman Leslie of the Ministry of Shipping , who showed that the Admiralty was relying on customs statistics that counted each arrival and departure , concluding that 2 , 400 vessels a week , translating into 300 ships a day , required an escort . In fact , there were only 140 ships per week , or 20 per day , on transoceanic voyages . But the manageability of the task was not the Admiralty ′ s only objection . It alleged that convoy 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 mine s . 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 . At a conference in February 1917 , some merchant captains raised the same concerns . 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 light of the cult of the offensive , the convoy was also dismissed a " defensive " . 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 limts [ 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 . In that month , the First Lord of the Admiralty — Eric Campbell Geddes — removed Admiral Jellicoe from his post of First Sea Lord because of the latter ′ s opposition to the convoy system , which Prime Minister David Lloyd George had appointed Geddes to implement . Organisation . Types of convoy . According to John Abbatiello , there were four categories of convoy used during World War I . The first category consists of the short - distance convoys , such as those between Britain and its European allies , and between Britain and neutral countries . The commercial convoys between England and the Netherlands or Norway are examples , as are the coal convoys between England and France . The second category consists of the escorts of warships , usually troopships , such as those from the Dominions in the early stages of the war . These formed the earliest convoys , but " probably the most overlooked category " . The British Grand Fleet itself could be included in this category , since it was always escorted by a destroyer screen in the North Sea and frequently by long - range " Coastal " and " North Sea " - class airships . The third category is the so - called " ocean convoys " that safeguarded transoceanic commerce . They traversed the Atlantic from the U . S . or Canada in the north , or from British or French colonial Africa or Gibraltar in the south . The fourth category is the " coastal convoys " , those protecting trade and ship movements along the coast of Britain and within British home waters . Most coastal and internal sea traffic was not convoyed until mid - 1918 . These convoys involved the heavy use of aircraft . Structure of command . With the success of the convoy system , the Royal Navy created a new Convoy Section and a Mercantile Movements Division at the Admiralty to work with the Ministry of Shipping and the Naval Intelligence Division to organise convoys , routings and schedules . Before this , the Norwegian convoys , coal convoys and Beef Trip convoys had often been arranged by local commanders . The Admiralty arranged the rendezvous , decided which ships would be escorted and in what order they would sail , but it left the composition of the escort itself to the Commander - in - Chief , Plymouth . The wing captain of the Southwest Air Group also received notification of the Admiralty ′ s convoys , and provided air cover as they approached their ports . The Enemy Submarine and Direction Finding Section and the code - breakers of Room 40 cooperated to give the convoy planners knowledge U - boat movements . With the advent of coastal convoys , escort composition and technique fell into the hands of the district commanders - in - chief . Use of aircraft . In April 1918 , the airship " NS - 3 " escorted a convoy for 55 hours , including patrols at night both with and without moonlight . In complete darkness the airship had to stay behind the ships and follow their stern lights . The only value in such patrols was in maximising useful daylight hours by having the airships already aloft at dawn . 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 . Testing of searchlights on aircraft revealed that the bomb payload needed to be much reduced to accommodate searchlight systems . Parachute flares offered better illumination ( and were less illuminating of the arships ′ positions ) , but they weighed in at 80 pounds each , making them too costly to drop unless the rough position of the enemy was already known . The Admiralty restricted the use of lights on airships for recognition , emergencies and under orders from senior naval officers only . 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 narrowling missing the third before escaping . The airship had been away at the time of the incident , which was one of the last of its kind . In 1918 , U - boats attacked convoys escorted by both surface ships and aircraft only six times , sinking three ships in total out of thousands . Because of the decentralised nature of the convoy system , the RNAS had no say in the composition or use of air escorts . 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 . Subsequent historians have not agreed , although they have tended to overstress the actual use made of aircraft in convoy escort duty . An Admiralty staff study in 1957 concluded that the convoy was the best defence against enemy attacks on shipping , and dismissed shore - based patrols while commending the use of air support in convoying .