The 556th SAW were the first US manned Radar Sites on Iceland. It originally started as a British station but as WW II intensified the United States sent troops to relieve the British in 1941. The American troops eventually grew to a total of 1471 personnel. Their primary mission was to direct anti-aircraft fire from the batteries attached to the group. They manned approximately 15 different locations scattered across Iceland. With the end of the war in Europe in 1945 the 556 Signal Aircraft Warning Battalion was decommissioned and the sites closed.
Their highly secret radars were rather crude and limited in range and ability but did prove successful in deterring Nazi attacks on Iceland and some of the shipping lanes in the North Atlantic. An interesting fact is that these radars operated on frequencies that are today used for television broadcasting.
Here are several pictures from the people who were stationed with the 556th. Winston Churchill visited and reviewed troops attached to the 556th and some of the pictures below document his visit.