The Japanese attack on Pearl Harbor on December 7, 1941 was the first foreign strike against U.S. territory since the war of 1812. While coast artillery units continued manning their forts early in the war, none ever fired a shot in anger. When it soon became apparent that aircraft and ships would be the main line of homeland defense, the Army transferred coast artillery officers and NCOs into field artillery, according to an About.com article.
During the war, the Army Air Forces and the Navy defended the homeland. Aircraft patrolled the approaches to ports looking for German and Japanese submarines. Navy destroyers and corvettes patrolled the sea lanes and pursued enemy craft that aircraft could not engage. The Navy even launched anti-submarine blimps to patrol the East Coast. At least one blimp attacked a German U-boat and was shot down for its effort.