Coast Guard historian Scott Price introduces the Coast Guard into WWI after U.S. declared war on Germany on April 6, 1917. Commandant Ellsworth Bertholf authorized the radio transmission "Plan One, Acknowledge" that placed the Coast Guard into a wartime footing. The Coast Guard was then transferred from the Treasury Department to the U.S. Navy, testing the Coast Guard's military capabilities and cementing the service as a military agency. U.S. Coast Guard video.