The Model-554 "Apache" Self-Propelled Artillery (known alternatively as the M554 Apache) is a heavy support vehicle operated primarily by the Army and Marine Corps of the UN Space Command. From its introduction in 2564 to its retirement in 2623, the Apache served as the primary means of artillery for UNSC forces, sans the orbital variety.
The Apache's longevity was achieved primarily through its numerous improvements and iterations. Four primary variants served as the most common types of the Apache. A number of special variants were also employed, the most popular of the latter being the M554D series, which sported a role more similar to that of a standard tank rather than artillery.
The M554A1 was the original member of the M554 family of vehicles. It sported the new VENOM Artillery Cannon, which fired the tenacious 165 millimeter exploding shell. The M554A1 proved especially useful against insurgent forces during the Second Human Civil War, often one of the keys to success in many battles involving shock and awe warfare.