Promoted to commander on 31 December 1948,[6] Janvrin was given command of the destroyer HMS Broadsword in 1951. Promoted to captain on 30 June 1954,[7] he was given command of HMS Grenville and the 2nd Training Squadron in 1957,[8] and the aircraft carrier HMS Victorious in 1959.[4] He was appointed Director of Tactical and Weapons Policy Division of the Admiralty Naval Staff from 1962 to 1963.