The Medium Tactical Vehicle Replacement (MTVR) 7-ton series of trucks was procured by the U.S. Marine Corps to replace their aging M809 and M989 series 5-ton Trucks. Besides having a higher load capacity then their predecessors, the MTVR also has better mobility as they are fitted with the TAK-4 Independent Suspension System. The MTVR series consists of the following types/variants:

Fielded Variants

-Mark 23/25: Standard Cargo Truck with/without Winch (6x6)

-Mark 27/28: Extended Cargo Truck with/without Winch (6x6)

-Mark 28C: Extended Truck Chassis with Engineer Specific Mission Modules. (6x6) Mission Modules include Earth Auger, Fuel Servicing, Water Distributer & Well Drilling.

-Mark 29/30: Dump Truck with/without Winch (6x6)

-Mark 31: Tractor (6x6)

-Mark 36: Wrecker (6x6)

-Mark 37: HIMARS Resupply Vehicle (with Material Handling Crane) (6x6)

Other Variants Available

-Short Bed Cargo Truck (4x4)

-9-Ton Cargo Truck with Load Handling System (LHS) (6x6)

-16.5-Ton Cargo Truck with LHS (8x8) 

Although the above variants were originally envisioned as being unarmored, battlefield realties emerged that demanded they also be fitted with armor protection.  The armor types developed were:

-Phase 1 (2003): Interim Add-On Armor. These kits were quickly developed through an Urgent Operational Request by the USMC and fitted in field depots.
-Phase 2 (2004): Armor Protection Kit (APK). An improved armor suite which was also fitted in USMC Depots.
-Phase 3 (2005): MTVR Armor Systems (MAS). Oshkosh mounted the Plasan Sasa ECP-58 armor protection kits during the production of these variants. 

Two (2) types of MAS were developed: a standard kit and one that allowed the cab armor to fold down for easier transport. Also, as it relates to the armored vehicles, any variant pre-built at the factory to easily install MAS later: (e.g. "Ready to Accept Armor"-RTAA) were originally designated "A1" (i.e. Mark 25A1).  Subsequently, when a vehicle was actually fitted with MAS, they are designated either "AMK" (which mounts the standard armor) or "AMK##A1" (with the reducible cab armor).