NDM-1 is a class of narrow gauge diesel locomotives built for Indian Railways in 1955. They are B+B diesel hydraulic locomotives.
Each locomotive consists of three sections, two identical four-wheeled bogies that are coupled together, with a cab suspended between the two. The only difference between the NDM1 class and the ZDM1 is the gauge. NDM1s are 2-foot (610 mm) gauge, the ZDM1s are 2-foot-6-inch (762 mm) gauge. Conversion between gauges (and thus classes) is possible and has been carried out on three locomotives.
When new, three (Jung 12109–12111), were built as 2 ft (610 mm) gauge NDM1s for the Matheran Hill Railway and numbered 501–503. The other four (Jung 12104–12108) were 2 ft 6 in (762 mm) gauge ZDM1s built for the Kalka–Shimla Railway and numbered 700–704. Number 700 was rebuilt to 2 ft (610 mm) gauge in 1976 and renumbered 500 and transferred to the Matheran Hill Railway. Three others followed later with 701–703 becoming 504, 506 and 505. The last ZDM1, 704, was moved to the Pragati Maidan exhibition centre.
Only 501 and 502 were to be found on the Matheran Hill Railway in 2016, with all the others believed to be withdrawn. 704 is now at the National Rail Museum in Delhi.
However, further variants of the class have been built by Indian Railways at Parel Workshops in Mumbai in recent years for service on the Matheran Hill Railway.
Numbers 550 and 551 were built in 2006 and designated Class NDM-1A. Number 400 was built in January 2016 with the designation NDM-1. This is the first of five similar new locomotives that reportedly have been promised for the line at a cost of Rs15 crore.