The steam locomotives of DR Class 99.77–79 were ordered by the Deutsche Reichsbahn in East Germany after the Second World War.

That led to a permanent shortage of locomotives on the Saxon narrow gauge lines, not least because the transportation requirement had grown considerably due to the mining of uranium in the Ore Mountains by the firm of Wismut AG.

They were given running numbers 99 771 to 99 794 and engines 12 "Patriot" & 13 "Pionier" (these 2 locomotives were built for the Mansfeld Mining Railway at Benndorf).

In order to enable brown coal firing, the grate area was increased compared with that of the Einheitslok.

Not until the 1980s did some locomotives end up on the Rügenschen Schmalspurbahn and Zittau network, in order to alleviate the shortage of engines there.