The K1A1, an upgraded version of the K1 MBT, was accepted into Korean service on 13 October 2001, after the first one was produced on 3 April 1996. The KM68 main gun has been replaced with the KM256 120 mm main gun (a licensed production model of the U.S. M256 which, in turn, is a licensed production model of the Rheinmetall L44) which nearly doubled the penetration power of the original vehicle. In addition, its fire control system, thermal sights, LASER rangefinder, turret and gun stabilization and armor have been improved, giving the vehicle greater survivability and lethality. The improved armor is called 'Korean Special Armour Plate (KSAP)'. The weight of the vehicle has increased along with the upgrade, and has slightly lowered its power-to-weight ratio and speed, the former of which was considered already too low for the rough Korean terrain by some critics.