"Centurion" was armed with a variety of weapons in June 1940 as the threat of German invasion increased and was then modified to serve as a repair ship for the local defence ships based in Devonport. In April–May 1941, she was converted into a blockship, with her magazines now serving as fuel tanks, but she was then modified with false gun turrets and masts to serve as a decoy for the battleship . Her armament now comprised two 2-pounder (40 mm) Mk II "pom-pom"s and eight Oerlikon light AA guns, all on single mounts. The ship's anti-aircraft armament was augmented in June 1942 with two additional "pom-pom"s and nine more Oerlikons.