 An ESG is composed of an amphibious assault ship (LHA/LHD), a dock landing ship (LSD), an amphibious transport dock (LPD), a Marine expeditionary unit, AV-8B Harrier II aircraft, CH-53E Super Stallion helicopters, CH-46E Sea Knight helicopters or more recently, MV-22B tiltrotors, and other aircraft that comprise a USMC composite squadron.Cruisers, destroyers, and attack submarines may deploy with either an expeditionary strike group or a carrier strike group.As originally envisioned in the 1990s, the ESG concept allowed the Navy to field 12 expeditionary strike groups and 12 carrier strike groups, in addition to surface action groups centered on "Iowa" class battleships.