The HK 94–100 is a series of four-axled, German Mallet locomotives with a 1,000 mm (3 ft 3+3⁄8 in) track gauge.

The locomotives did not continue in military service, however, due to the end of the war, and were handed over to various private railways, some as substitutes for locomotives that had been commandeered for wartime service.

The locomotive is externally very similar to the other Mallet engines, only the driver's cab is noticeably different, and all axles are mounted in inside frames (the older engines have an outside frame for the rear two axles).

The rear set of drivers with their high-pressure cylinders is fixed in the plate frame of the loco.

The front set of drivers with their low-pressure cylinders are linked to the rear sets with king pins, the rivetted boiler lies on it with its slide plates (Gleitplatten) Leaf springs at the sides hold the driving gear in a central position.