Selective Service Act He knew—and the Kriegsmarine reminded him in the most strenuous terms—that a crossing and follow-on supply operation could not be made into the teeth of the Royal Air Force (RAF) and Royal Navy simultaneously He therefore set as a precondition of invasion prior destruction of the RAF Only if Luftwaffe air superiority was established could the Kriegsmarine escort an invasion force across the Channel with any chance of success, against British naval and air squadrons sure to resort to near-suicidal measures in defense While the Battle of Britain was fought in the sky that summer, river barges and other makeshift invasion transports were assembled and landings practiced, though without much enthusiasm from the Heer or Kriegsmarine Failure of the Luftwaffe to suppress the RAF was compounded by Kriegsmarine hesitation and repeated postponement of possible invasion dates, to September 15 or later A key turning point came when German bombers stopped assaulting RAF radars and airfields and began bombing London on August 24, leading RAF Bomber Command to retaliate by hitting Berlin It appears this switch in bombing tactics vitiated Hitler’s plan to terror bomb London only during the landings, so that the city’s population would panic and clog roads in southern England with refugees Instead, Luftwaffe losses over London and other cities quickly became intolerable Hitler turned away from the air battle and from invasion on September 14, leaving the Luftwaffe to bomb on a lesser scale during the first Blitz campaign Hitler set an ostensible new landing date of September 27, but most historians believe that he decided by mid-September not to invade Britain in 1940 Hitler was already thinking about “Operation OTTO,” his great attack on the Soviet Union by which he intended to deny Britain its last potential ally on the continent and bring about acceptance of his hegemony Later renamed Operation BARBAROSSA, he launched that fateful assault on June 22, 1941 Certain he would win a decisive victory in the east, even as the OKW was planning final details of BARBAROSSA Hitler ordered resumption of a landing craft program for the second half of 1941 Its aim was to have enough boats ready to carry out an invasion of Britain in 1942 SEELOW HEIGHTS See Germany, conquest of SELASSIE, HAILE (1892–1975) See Abyssinia; Abyssinian War (1935–1936); East African campaign (1940–1941); Gideon Force SELECTIVE SERVICE ACT Narrowly passed by Congress and signed by President Franklin D Roosevelt on September 16, 1940, this legislation raised the authorized strength of the U.S Army to 1.4 million men Over the next year 17 million men registered for military service in the first ever peacetime “draft” in American history Still, it was not until after Pearl Harbor (December 7, 1941) that Congress lifted most restrictions on the numbers of conscripts who could be actually inducted for training and service, and even then large numbers were exempted for factory or farm 970