<P> The first transatlantic convoy left Hampton Roads on 24 May escorted by the armored cruiser HMS Roxburgh, 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 . </P> <P> Losses in convoy dropped to ten percent of those suffered by independent ships . 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 . </P> <P> 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 . </P> <P> 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 . </P>

Why did they have to have supply convoys in ww1