The submarine was laid down at the Chantiers et Ateliers Augustin Normand yard at Le Havre on 9 June 1932. She was launched on 15 September 1935, and commissioned on 20 September 1937. Under the command of Lieutenant de vaisseau Jaume from August 1939, Junon operated from Oran and Casablanca early in the war, finally sailing to France in March 1940 for refitting. Querville was promoted to Capitaine de frégate in July 1941, and in August Junon became the flagship of the 1ère Division de sous-marins des FNFL (1st Free French Submarine Division), along with Minerve and Rubis.