Narrow-gauge locomotives of India
This is a list of narrow-gauge locomotives that have been or are being operated by Indian Railways. All railways except the heritage ones are closed or under conversion/are converted to the nation-wide standard  gauge, under Project Unigauge. So narrow-gauge locomotives are operating only on the heritage routes as of 2021. General
Diesel locomotive classes  

 ZDM-1: This locomotive was built by Arn. Jung. These were called the class DZ on NR (Kalka-Shimla Railway). This was a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge. It was identical to NDM-1 class with 2'0" gauge. Only four of these locos were regauged to 2'0" gauge and converted to NDM-1 units. The ZDM-3 locos were available in (1972-1982). The fifth loco NR #704, was used at Pragati Maidan in New Delhi, where it was used to haul a short train with the name Pragati Express with  aluminium-bodied coaches on a 1.5km figure-8 track at an exhibition centre specially during IITF. Loco numbers were not written on the body of the loco. ZDM-2: This was a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge. These loco were mainly used in Nainpur-Gondia section narrow-gauge route. All the locomotives are retired/withdrawn from service. ZDM-3: This is a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge of Indian Railways. These locomotives can be found on the routes of Kalka-Shimla route and Kangra Valley route. ZDM-4: These locomotives were built by CLW and they were the modified version of ZDM-3 class with an extra axle to reduce axle load (1-B-B-1 bogies). But this extra axle caused wheel slip. These locomotives can be found on routes like Kangra Valley and were found earlier on the Nagpur narrow-gauge routes and Raipur narrow-gauge routes. This is a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge. ZDM-4A: This was a variant of the ZDM-4 loco. This loco was used in Barsi Light Railway. These 1-B-B-1 locos had a 700hp power-pack. In 1996 one of these was sent to Nepal Jayanagar-Janakpur railway line. This was a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge. ZDM-5: This locomotive was one of the powerful narrow-gauge locomotives of the world. These locomotives were operated on routes like Pratapnagar narrow-gauge and Dhaulpur narrow-gauge routes. Four locos of this class were sent to work on Jayanagar-Janakpur railway in Nepal in 1994. All the locomotives are retired/withdrawn from service. This was a narrow-gauge locomotive with 2ft 6in (762 mm) wide gauge. NDM-1: This is a articulated locomotive with two prime movers. But in case of uphill travel it uses both its engines and in case of downhill it uses one engine on Neral-Matheran line. It was originally intended to be used in Kalka-Shimla route. This is a narrow-gauge locomotive with 2ft 0in (610 mm) wide gauge. When Kalka-Shimla route was regauged ZDM-3 was obtained for that route. NDM-5: These locomotives were used on Central Railways Gwalior narrow-gauge route. These locomotives were based on another narrow-gauge locomotive called ZDM-5. It had been equipped with dual brake system. All the locomotives are retired/withdrawn from service. This was a narrow-gauge locomotive with 2ft 0in (610 mm) wide gauge. NDM-6: This locomotive was originally intended for Matheran Hill Railway but for some reason it was then allocated to Darjeeling Himalayan Railway. Only six of these locomotives have been made and all are in service on Darjeeling Himalayan Railway. This is a narrow-gauge locomotive with  gauge. NBM-1: This locomotives were used on Central Railways Gwalior narrow-gauge route. These were the battery electric locomotives which are similar to YAM-1 locomotives. Only three units were built in 1987. All the locomotives are retired/withdrawn from service. This was a narrow-gauge locomotive with 2ft 0in (610 mm) wide gauge. Specifications

Units produced and in service

