Star Trek: Enterprise
Episode: ENT 053 - Xindi, The

Acronym for "Military Assault Command Operations,? a specially trained combat wing of the Earth military, apart from the Starfleet space service and its security officers. A unit of MACOs under Major Hayes is assigned to Captain Archer's NX-01 Enterprise for the Xindi mission, and enjoys a testy shipboard rivalry with Lieutenant Reed's security officers.