The American military arrived in England during the second world war when they formally joined the allies in the fight against Germany, Italy and Japan. Initial agreements were made with the United States Airforce in January and March 1941. The Japanese attack on Pearl Harbour occurred on 7th December 1941. The first US forces base in England was at RAF Dawes Hill in High Wycombe and that commenced on 22nd February 1942. Nazi Germany surrender and 8th May 1945 was marked as Victory in Europe Day. Atomic bombs were dropped on Hiroshima (6th August 1945) and Nagasaki (9th August 1945) with the Japanese surrender being announced on 15th August 1945. The conflict which gave rise to the arrival of United States military activity having bases in England had come to an end. Some seven decades later the US military are still operating from bases in England.
The legal basis for the US Visiting Force in the United Kingdom is primarily the North Atlantic Treaty Organisation (NATO) Status of Forces Agreement of 1951 (SOFA) and the Visiting Forces Act of 1952.