A member of a United States Coast Guard (USCG) Maritime Security Response Team (MSRT), covers a doorway with his M4 CQBR carbine during close quarters combat (CQC) training.
Maritime Security Response Teams are a component of USCG's Deployable Operations Group.
MSRTs specialize in maritime counter terrorism operations such as rescuing hostages from a hijacked ferry or retaking a capture oil / gas platform from terrorists.
MSRT operators undergo extensive training in CQC and various insertion methods such as vertical insertion from helicopters and boarding vessels / installations from small boats.