The situation drastically changed in early 1943, when Palermo became a target for USAAF bombers operating from newly conquered bases in French North Africa. The USAAF used larger numbers of bombers, and frequently made use of Boeing B-17 and Consolidated B-24 heavy bombers as opposed to the medium bombers previously used by the British. Air raids on Palermo escalated in both frequency and intensity, initially as the Allies sought to hamper the use of its harbour for supply convoys bound for Tunisia, and later in preparation for the invasion of Sicily.