Defence Secretary Des Browne has been criticised for not discussing in parliament plans to allow the US military to use RAF Menwith Hill in North Yorkshire for ballistic missile defence.
USAF F15 C Eagle fighter at RAF Lakenheath
The Ministry of Defence says that the Menwith Hill deal "continues the tradition of cooperation in support of UK, US and allied interests", which dates back to 1941.
Mr Browne said the work at Menwith Hill would support the existing UK-US missile warning mission, and enable satellite data to be passed into the new US missile defence system.
The United States Air force has two major commands based outside continental North America. The United States Air Force in Europe Command (Usafe) has units at several UK locations. The other is the Pacific Air Forces Command - its headquarters is based in Hawaii.
Meanwhile US military personnel are based in two UK territories overseas - Diego Garcia and Ascension island.
RAF Mildenhall and its sister station Lakenheath, in Suffolk, are the two largest US air bases in the UK.
Mildenhall is home to several airborne units including the 100th Air Refuelling Wing and the Air Special Operations Command and is also the base for some US navy aircraft.
Meanwhile Lakenheath provides the base for F15 Eagle aircraft from the 48th, or Liberty fighter wing, as well as PaveHawk helicopters.
The US government also has a small number of staff at RAF Fylingdales, in North Yorkshire as a missile early warning station.
B52 bomber taking off from RAF Fairford
RAF Fairford in Gloucestershire has been used by American B-52 bombers flying on missions to the Gulf.
And there are US aircraft or personnel based at RAF stations at Alconbury, Upwood and Molesworth, in Cambridgeshire, known as the 'tri-base area'.
Northamptonshire is home to RAF Croughton a USAF communications base, Welford on the Berkshire-Wiltshire border is a large ammunition compound.
US military personnel have been based at many British military establishments
The United States military operates out of two overseas British territories. Diego Garcia, about 1,000 miles south of India is a British Indian Ocean Territory, which provides a navy support facility.
The base at Ascension island, another British overseas territory, which lies 1,000 miles west of Africa is used jointly by the RAF and USAF. The RAF uses it as a gateway to the Falkland Islands, American counterparts use it as a stopping off point when crossing the Atlantic.