NWE Nos. 6 and 7, later Class 99.610, are narrow gauge tank locomotives with a C axle arrangement that belonged to the Nordhausen-Wernigerode Railway.
The two engines had been supplied to the Army Technical Research Institute ("Heerestechnische Prüfungsanstalt") but were transferred in 1917 (superheated steam engine) and 1921 (saturated steam engine) to the Nordhausen-Wernigerode Railway as NWE 6 and NWE 7.
NWE 7 had previously worked as Locomotive No. 15 with the Nassau Light Railway.
Until the 1980s, both engines were used around Wernigerode by the Deutsche Reichsbahn, their last duties being in Rollbock service. The DR gave them new numbers following their nationalisation. Although they had been taken out of service, the Harz Narrow Gauge Railways took both engines over.
Only 99 6101 is currently in working order.