The Coast Guard is a maritime, military, multi-mission service unique among the U.S. military branches for having a maritime law enforcement mission (with jurisdiction in both domestic and international waters) and a federal regulatory agency mission as part of its mission set. It operates under the Department of Homeland Security during peacetime, and can be transferred to the Department of the Navy by the President at any time, or by Congress during time of war.
My ship. USS Conyngham DDG-17. Adams class destroyer (guided missile). I served aboard her from 1985-89. She caught fire and burned at sea in 1990. The crew managed to get her back to port but she was decommissioned immediately, sold for scrap and torn down in 1994. In my mind's eye, however, she's still out there sailing.