The neutral United States moves closer to war with Germany when U.S. forces land on Iceland to take over its garrisoning from the British. From thereon, the U.S. Navy had the responsibility of protecting convoys in the nearby sea routes from attack by German submarines. With Iceland and its nearby sea routes under U.S. protection, the British Royal Navy was more free to defend its embattled Mediterranean positions.
The occupation of Iceland came less than a month after President Franklin D. Roosevelt froze all German and Italian assets in the United States and expelled the countries' diplomats in response to the German torpedoing of the American destroyer Robin Moor. Much of the North Atlantic was now in the American sphere, and U.S. warships patrolled the area for German submarines, notifying London of all enemy activity. The United States officially entered World War II after Japan attacked the Pearl Harbor naval base in Hawaii in December 1941.