<P> On 16 June 1941, after negotiation with Churchill, Roosevelt ordered the United States occupation of Iceland to replace the British invasion forces . On 22 June 1941, the US Navy sent Task Force 19 (TF 19) from Charleston, South Carolina to assemble at Argentia, Newfoundland . TF 19 included 25 warships and the 1st Provisional Marine Brigade of 194 officers and 3714 men from San Diego, California under the command of Brigadier General John Marston . Task Force 19 (TF 19) sailed from Argentia on 1 July . On 7 July, Britain persuaded the Althing to approve an American occupation force under a U.S. - Icelandic defense agreement, and TF 19 anchored off Reykjavík that evening . U.S. Marines commenced landing on 8 July, and disembarkation was completed on 12 July . On 6 August, the U.S. Navy established an air base at Reykjavík with the arrival of Patrol Squadron VP - 73 PBY Catalinas and VP - 74 PBM Mariners . U.S. Army personnel began arriving in Iceland in August, and the Marines had been transferred to the Pacific by March 1942 . Up to 40,000 U.S. military personnel were stationed on the island, outnumbering adult Icelandic men (at the time, Iceland had a population of about 120,000 .) The agreement was for the US military to remain until the end of the war (although the US military presence in Iceland remained through 2006, as postwar Iceland became a member of NATO). </P> <P> American warships escorting Allied convoys in the western Atlantic had several hostile encounters with U-boats . On 4 September, a German U-Boat attacked the destroyer USS Greer off Iceland . A week later Roosevelt ordered American warships to attack U-boats on sight . A U-boat shot up the USS Kearny as it escorted a British merchant convoy . The USS Reuben James was sunk by U-552 on 31 October 1941 . </P> <P> On 11 December 1941, Adolf Hitler and Nazi Germany declared war against the United States, the same day that the United States declared war on Germany and Italy . </P> <P> The established grand strategy of the Allies was to defeat Germany and its allies in Europe first, and then focus could shift towards Japan in the Pacific . This was because two of the Allied capitals (London and Moscow) could be directly threatened by Germany, but none of the major Allied capitals were threatened by Japan . Germany was the United Kingdom's primary threat, especially after the Fall of France in 1940, which saw Germany overrun most of the countries of Western Europe, leaving the United Kingdom alone to combat Germany . Germany's planned invasion of the UK, Operation Sea Lion, was averted by its failure to establish air superiority in the Battle of Britain . At the same time, war with Japan in East Asia seemed increasingly likely . Although the U.S. was not yet at war with either Germany or Japan, it met with the UK on several occasions to formulate joint strategies . </P>

When did us start fighting in europe ww2