<P> The Battle of Britain began in early July with Luftwaffe attacks on shipping and harbours . Britain rejected Hitler's ultimatum, and the German air superiority campaign started in August but failed to defeat RAF Fighter Command . Due to this the proposed German invasion of Britain was postponed indefinitely on 17 September . The German strategic bombing offensive intensified with night attacks on London and other cities in the Blitz, but failed to significantly disrupt the British war effort and largely ended in May 1941 . </P> <P> Using newly captured French ports, the German Navy enjoyed success against an over-extended Royal Navy, using U-boats against British shipping in the Atlantic . The British Home Fleet scored a significant victory on 27 May 1941 by sinking the German battleship Bismarck . </P> <P> In November 1939, the United States, who were taking measures to assist China and the Western Allies, amended the Neutrality Act to allow "cash and carry" purchases by the Allies . In 1940, following the German capture of Paris, the size of the United States Navy was significantly increased . In September the United States further agreed to a trade of American destroyers for British bases . Still, a large majority of the American public continued to oppose any direct military intervention in the conflict well into 1941 . </P> <P> In December 1940 Roosevelt accused Hitler of planning world conquest and ruled out any negotiations as useless, calling for the US to become an "arsenal of democracy" and promoted Lend - Lease programmes of aid to support the British war effort . The US started strategic planning to prepare for a full scale offensive against Germany . </P>

In 1939 the immediate response of the united states to the start of world war 2 in europe was to
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