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 surface speed was 12 knots and submerged could reach nine. She could dive to periscope depth in 45 seconds.