The U.S. Navy is the branch of the military responsible for operations at sea. The Navy also uses aircraft in its operations, and it often works together with the Marine Corps.
The U.S. Marine Corps has served in every armed conflict in which the United States has been involved. Marines engage in military operations, peacekeeping missions, and provide humanitarian aid.
The Coast Guard is the only branch of the military responsible for enforcing the law, in both the United States and in international waters. During time of war, the Coast Guard can be placed under the control of the U.S. Navy.