The class K locomotives were a complete success which brought the reign of the (super reliable, but multi-section) class B’s to an end (not to be scrapped, but ongoing new locomotive orders would be single-unit machines instead of the 2-unit design of the B family) but the weight balance of the drivetrain wasn’t quite as good as the operating department wanted, so for the new class K2 had everything shuffled around to put the radiators next to the streamlined cab and the pantographs at the boxcab end of the unit.

The 2003 K2b model shares electrical components with the (slightly more powerful) K4s, so produce 6600 HP instead of 6500; there are no external differences between them and the original K2s.