Computer operation is controlled by an internally stored program which is loaded from a magnetic tape cartridge at the launch facility (LF). Both the D37D computer and the MGC are designed and programmed to control the Minuteman III missile throughout the powered portion of flight. After thrust termination they also control the PBV for the reentry vehicle (RV) deployment phase. In addition, they control the alignment of the inertial platform and test/monitor the guidance & control (G&C) system and other components to determine continued readiness while missiles are in alert status. The D37D computer began to be replaced by the MGC in 2000 as part of the Guidance Replacement Program (GRP), with fielding planned through 2008. The MGC incorporates the amplifier assembly functions.