By October 1942, Davidson was a colonel and assistant chief engineer for the Western Task Force of Operation Torch of the Allied North Africa under the command of General George S. Patton. As 1st Armored Division moved to invade Sicily in June 1943, it was activated into Seventh United States Army, and Davidson became its chief engineering officer. As a combat engineer, he facilitated Seventh Army's landing in Sicily and enabled Patton's armor to move rapidly across enemy territory. An appreciative Patton used one of his own general stars to honor Davidson in a September 1943 battlefield promotion to brigadier general, one of the youngest of the war at age 39. Davidson remained with Seventh Army under its interim command by General Mark W. Clark then General Alexander Patch and was key in planning for Operation Anvil / Operation Dragoon, the Allied landing in southern France following the D-Day invasion of Normandy in June 1944. He continued with the Seventh Army in its move through Germany. At the conclusion of the war he was an engineer with the post-war occupation Fifteenth United States Army and served as president of the first Nuremberg War Crimes Tribunal for military defendants.