The M172 Archer is a 155mm Self-Propelled Gun based on the chassis of the M28A5 MBT. The Archer is armed with an autoloaded, unmanned turret placed at the rear of the vehicle. The SPG is manned by a crew of three: a commander, gunner, and driver. The vehicle contains twelve shots within the turret, and an additional twelve shots within the vehicle can resupply the gun from the inside. Usually, an M125-based ammunition carrier will accompany each vehicle. The M172 is only Armored to resist 30mm rounds from the front and 14.5mm rounds everywhere else. The tank is powered by the Honeywell ATG6200 turbine and shares 99% of drivetrain components with the M28A5. The M172 is slated to enter service along with the M173 203mm SPG in artillery battalions.