After attending promotion courses in 1932 he joined the Royal Navy Submarine Service the following spring, 1933. He served at Gosport and undertook intensive training on submarines. In September he served in the submarine which was part of the Mediterranean Fleet. It was his first appointment as a submariner. In 1934 he accompanied his new post on trips around the Mediterranean. Visits to Gibraltar, Malta, Algeria, France and Italy followed. In October 1934 he transferred to HMS "L56" based with the rest of the 6th Submarine Flotilla at Portsmouth. Wanklyn spent a year on board before becoming the boat's first lieutenant. He learned a number of officer functions and was responsible for the vessel's diving trim and crew discipline. He would recall the performance of the L-class submarine when he commanded other such vessels in early 1940. He served aboard HMS "Shark" for the majority of 1937 and 1938 and became her first lieutenant.