The United States' Posse Comitatus Act, passed in 1878, prohibits any part of the Army or the Air Force (since the U.S. Air Force evolved from the U.S. Army) from engaging in domestic law enforcement activities unless they do so pursuant to lawful authority. Similar prohibitions apply to the Navy and Marine Corps by service regulation, since the actual Posse Comitatus Act does not apply to them. The Coast Guard is exempt from Posse Comitatus since it normally operates under the Department of Homeland Security versus the Department of Defense and enforces U.S. laws, even when operating as a service with the U.S. Navy.