War Wanklyn was then appointed as the commanding officer of HMS H31 on 5 February 1940. H32 conducted several exercises throughout the next few months and refitted in April. By July 1940 the situation had worsened for the Royal Navy. On 14 May the Dutch capitulated. Belgium surrendered on 28 May and France collapsed on 22 June 1940. Some 14 submarines had been lost and the British Army evacuated from Norway in the same month. It left the navy defending British waters against a hostile coastline which ran from northern Norway to the French Atlantic Ocean coast. The Royal Navy prepared itself for a possible German invasion of Britain should the Royal Air Force fail in the Battle of Britain. It was also busy defending sea communications in the English Channel—during the Kanalkampf—and the Battle of the Atlantic. North Sea operations To exert pressure on German naval forces Wanklyn undertook a patrol on 14 July. On 18 July he arrived off the Dutch coast. North of Terschelling Island he sighted three anti-submarine trawlers in formation. After spending an hour closing on the vessels he launched a single torpedo at 07:37, from a range of 900 yards, on a 125 degree track angle to bring all the ships nearly in line with the torpedo and maximise a chance of a hit. He heard the torpedo through the hydrophones. Two minutes later there was an explosion and the German submarine chaser UJ-126 sank. For the next thirty minutes eight depth charges were directed at the submarine, the nearest detonating 250 yards away, before the enemy gave up and retired eastward. A curt statement in his report marked the victory: "The behaviour of the crew was most satisfactory." Wanklyn returned to port in Blyth. His success was to be rewarded in August 1940. Wanklyn was relocated to the north-west, to Barrow-in-Furness, where he was presented with the command of , which was then under construction. He commanded her for the remainder of the war. Upholder was a U-class submarine equipped with four internal and two external torpedo tubes. These were supplemented by a 76 mm QF 3-inch 20 cwt deck gun. She was laid down on 30 October 1939 and launched in July 1940. Wanklyn took command just as she was completed and watched over the ship during her construction. The vessel was 196 feet long with a beam of 12 feet. Her