Final answer:
The U.S. Coast Guard operates under the Department of Homeland Security; however, during wartime, it can operate under the Department of Defense, with the President as the Commander in Chief.
Step-by-step explanation:
During wartime, the U.S. Coast Guard operates directly under the Department of Homeland Security. It is one of the armed forces of the United States, which also include the Army, Navy, Marine Corps, and Air Force. These forces are overseen by civilian authorities, with the President serving as the Commander in Chief. In peacetime, the Coast Guard is under the Department of Homeland Security but during wartime or by order of the President, it can come under the command of the Department of Defense through the Navy. The Coast Guard's integration into the armed forces helps secure the territory of the United States and effectively contributes to the war effort both at home and abroad.