The German Class 99.73-76 engines were standard locomotives (Einheitslokomotiven) in service with the Deutsche Reichsbahn for Saxony's narrow gauge railways.

So it fell to the newly formed Reichsbahn railway division of Dresden to procured an Einheitslok with a 750 mm (2 ft 5+1⁄2 in) track gauge.

According to the supply agreement, the Sächsische Maschinenfabrik was supposed to deliver more locos, but as a result of its bankruptcy and liquidation in 1930, this order was transferred to the Berliner Maschinenbau AG (BMAG), previously Schwartzkopff.

The engines fulfilled expectations; by double-heading it was now possible to haul even very long (up to 56 axles) narrow gauge trains uphill.

At the same time, there was an enormous increase in the transportation required in the Ore Mountains as a result of new uranium mines opened by SDAG Wismut.

Because Heberlein brakes were still partially in use at that time, the locomotives also had, on delivery, the necessary equipment for them, complete with guide rollers and winders (Haspel).