Complex sentence: The U.S. Navy turned the base over to the Danish Navy in August 1951 and, during the early years of the Cold War, the base was used by anti-submarine warfare (ASW) ships of NATO, which tracked Soviet Navy submarines in the North Atlantic.
Split into simpler sentences: The U.S. Navy turned the base over to the Danish Navy in August 1951. During the early years of the Cold War, the base was used by anti-submarine warfare (ASW) ships of NATO, which tracked Soviet Navy submarines in the North Atlantic.