But relief efforts are just a part of what the Coast Guard does. The Coast Guard. which is a part of the Department of Homeland Security. is the lead federal agency for maritime homeland security. The Homeland Security Act of 2002 specifies five homeland security missions for the Coast Guard: ports. waterways. and coastal security. drug interdiction. migrant interdiction. defense readiness. and other law enforcement duties. With regard to port security. the Coast Guard is responsible for evaluating. boarding. and inspecting commercial ships approaching U.S. waters. countering terrorist threats in U.S. ports. and helping protect U.S. Navy ships in U.S. ports.