Within the US Army hierarchy, some senior officers questioned the practicality of airborne forces as a combat entity. The Germans had successfully used airborne forces during the invasions of the Netherlands in May 1940 and Crete in May 1941. Wartime was proving tough for American airborne forces. In November 1942, as part of Operation Torch in the North African campaign, US paratroopers who missed their drop zone (DZ) marched to capture an airfield already in the hands of friendly forces. During the Allied invasion of Sicily in July 1943, US paratroopers once more landed far from their intended targets. But the real tragedy came when friendly fire brought down 23 aircraft and damaged 37 more; 318 paratroopers and airmen were killed or wounded. The poor performance of American airborne forces in Sicily prompted Lieutenant General Dwight D. Eisenhower to recommend to General George C. Marshall, the US Army Chief of Staff, that division-size airborne units were too difficult to control in combat.