As WWII closed, the Air Staff decided to preserve the UK's electronic intelligence (ELINT) expertise, resulting in the formation of the Radio Warfare Establishment and later the Central Signals Establishment. A tentative ELINT program was commissioned in 1946 using a small number of Lancaster and Mosquito aircraft specially modified for the task and as relations with the Soviet Union deteriorated, interest focused on the growing Soviet air defense system, with the 1948 Berlin crisis resulting in the first major ELINT program against the Soviet Union's air defenses.