'Magnet' was the Allied programme to start the build-up of US ground forces in Northern Ireland as part of the development toward subsequent operations on the European mainland (January/May 1942).

The British and US military staffs agreed during their ABC-1 meetings in Washington between January and March 1941 to exchange military missions in order to facilitate the planning for the eventuality of a US entry in the war. Major General James E. Chaney, a US Army Air Corps officer, arrived in the UK on 18 May 1941, and on the following day the Headquarters, Special Observer Group (SPOBS), was established in London with the additional role of studying British use of Lend-Lease supplies. Chaney’s formal designation was the Special Army Observer in the UK and head of SPOBS. After the US entry into the war in December 1941, the SPOBS was redesignated as the US Army Forces in the British Isles (USAFBI). At the time of the 'Arcadia' Conference of December 1941/January 1942, the decision was made to place the 'Magnet' forces (the US Forces for Northern Ireland) under the command of Major General Edmond L. Daley, who was responsible to Chaney, who had been designated as the commanding general, USAFBI. Lieutenant General John C. H. Lee became chief of the Services of Supply, USAFBI, and later deputy theatre commander of the European Theater of Operations, US Army which, on 8 June 1942, became the successor to USAFBI. Its mission was to conduct planning for the eventual retaking of Europe and to exercise administrative and operational control over US forces.

The 133^rd Infantry of Major General Russell P. Hartle’s 34^th Division was the first US Army unit sent to Europe in World War II. The regiment’s first battalion reached Belfast in Northern Ireland late in January 1942, and was followed by the rest of the regiment in February. These units were designated as US Army Northern Ireland Forces, later incorporated into the ETOUSA. The The 133^rd and 168^th Infantry trained in the peat bogs, and performed border guard patrols between Northern Ireland and the neutral Irish Free State. The remaining unit of the division, the 135^th Infantry, arrived in May 1942.