During the invasion of mainland Italy in late 1943, beginning the Italian Campaign, 55 HAA Rgt at first remained in Sicily defending Augusta. Later, as the Allied armies advanced, the AA units followed to protect vital airfields and ports in the rear. 55th HAA Regiment crossed to Italy to join 52 AA Bde stationed at the airfield complex around Foggia. It later moved to 66 AA Bde supporting the advance of US Fifth Army particularly the Salerno bridgehead and airfields. After the breakout from Anzio in May 1944, 66 AA Bde took over that area, and then followed Fifth Army up the west coast through Rome until it reached Livorno, where 55 HAA Rgt defended the important supply port. During the winter of 1944–45, 55th HAA Rgt was transferred to 12 AA Bde, supporting British Eighth Army.