The U.S. Coast Guard operates as part of the U.S. Department of Transportation during peacetime. In times of war, or when the president so directs, it operates under the Department of the Navy. The Coast Guard is the principal federal agency for national maritime transportation policy and for marine safety and maritime law enforcement on the high seas and in all waters under the jurisdiction of the United States.

Today its mission is global in scope and includes the following tasks: developing construction standards and operational rules for American deep water ports; conducting International Ice Patrol in the North Atlantic; cooperating with Drug Enforcement Administration and Customs Service to detect and intercept drug smugglers; providing patrol and law enforcement in the 200-mile Fishery Conservation Zone off the coasts of the United States; and performing ice-breaking services for commercial and scientific ships in the Great Lakes, Gulf of Alaska, and in the Arctic and Antarctic.