Nazi Germany and demanded rearmament, became prime minister after his predecessor Neville Chamberlain's policy of appeasement had totally collapsed and Britain was unable to reverse the German invasion of Norway in April 1940. After the fall of France in June 1940, Roosevelt gave Britain and (after June 1941) the Soviet Union all aid short of war. The Destroyers for Bases Agreement which was signed in September 1940, gave the United States a 99-year rent-free lease of numerous land and air bases throughout the British Empire in exchange for the Royal Navy receiving 50 old destroyers from the United States Navy. Beginning in March 1941, the United States enacted Lend-Lease in the form of tanks, fighter airplanes, munitions, bullets, food, and medical supplies. Britain received $31.4 billion out of a total of $50.1 billion sent to the Allies. Roosevelt insisted on avoiding the blunder that Wilson had made in the First World War of setting up the financing as loans that had to be repaid by the recipients. Lend lease aid was freely given, with no payments. Also there were also cash loans were repaid at low rates over a half-century. Summit meetings became a standard practice starting with August 1941, when Churchill and Roosevelt met on British territory, and announced the Atlantic Charter. It became a fundamental document—All the Allies had to sign it—and it led to the formation of the United Nations. Shortly after the Pearl Harbor attack, Churchill spent several weeks in Washington with the senior staff hammering out wartime strategy with the American counterparts at the Arcadia Conference. They set up the Combined Chiefs of Staff to plot and coordinate strategy and operations. Military cooperation was close and successful. Technical collaboration was even closer, as the two nations shared secrets and weapons regarding the proximity fuze (fuse) and radar, as well as airplane engines, Nazi codes, and the atomic bomb. Millions of American servicemen were based in Britain during the war. Americans were paid five times more than comparable British servicemen, which led to a certain amount of friction with British men and intermarriage with British women. In 1945 Britain sent a portion of the British fleet to assist the planned October invasion of Japan by the United States, but this was cancelled when Japan was forced to surrender unconditionally in August. India Serious tension erupted over American demands that India be given independence, a proposition Churchill