The M1A2 Abrams program included improved frontal armor protection, improved mission electronics on the digital data bus, and the introduction of an independent thermal sight (ITS) (the M1A1 had a mount in place, but it was never used until the M1A2 upgrade). Although 77 new M1A2s rolled off the production line, most were retrofits for the rebuilt Abrams. The next stage of improvement was the System Enhancement Package (SEP), which added navigation and situational awareness. The additional electronics of the mission required an improvement in the cooling system, which increased the electrical load on the tank. For the operation of the tank without a constantly working main engine, an auxiliary power plant was added in the rear basket of the tower. Further improvements came with SEP v2 (Version 2), which added improved mission electronics, improved transmission and the ability to mount a Common Remotely Operated Weapons Station (CROWS). The external APU was supposed to be moved inside the hull, but the APU was replaced with batteries that provided extended power with the engine off. SEP v3 is under development, replacing the batteries with an in-body diesel generator and additional mission system upgrades.
