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The ALCO DL560C is a passenger/freight-hauling diesel-electric locomotive with AC electric transmission designed by the American Locomotive Company and produced under license by Diesel Locomotive Works (DLW) of Varanasi, India for Indian Railways as their classes WDM-2, WDM-3A/2C, WDM-3D and WDG-3A for operation in India. The locomotive is fitted with a 16-cylinder ALCO 251 B,C diesel engine. In the early 1960s Indian Railways needed a reliable diesel workhorse to gradually replace its steam locomotive fleet. Equal numbers (40 each) of ALCO's DL560C and EMD's SD24 were chosen for trials. More locomotives of each of these were purchased for more trials. Indian Railways was keen on producing these locomotives in the country rather than depending on imports. EMD did not agree for a Transfer-of-Technology, while ALCO did. Thus ALCO DL560C was chosen for the job due to its easy maintenance, reliability and simple operation. And from then on vast numbers of this loco in different configurations have been produced and they still[when?] continue to dominate the diesel route of Indian Railways.
There are four main variants of this loco, which are extensively modified for particular needs. They are, as follows:
The first loco of the type DL560C to arrive in India is WDM-2. Initial batches arrived from the ALCO manufacturing facility in ready-to-ride condition. And 12 more arrived from ALCO in, to be assembled kits. This loco remained as the workhorse of Indian Railways in the 20th century. This loco solely can haul 9 passenger and can haul 18 with the help of another WDM-2. This model had a maintenance schedule of 3000 km/10days. Later on, improving the fluid level and bearings, the schedule was increased to 30 days. The gear ratio being 65:18 and having a max speed of 120 km/h. JUMBOS (full-width short hood) and WDM-2A/2B are some of WDM-2s variants with minor modifications. The production began in the late 1960s, and went on till the late 1990s. They are being eventually retired. They belong to series 18xxx, 17xxx and 16xxx.
WDM-3A, previously known as WDM-2C, are more powerful than the previous WDM-2 version by 500 hp. The first loco was delivered in 1994. This loco was capable of doing the work of two WDM-2S. They too had a top speed of 120 km/h. The gear ratio is same as that of WDM-2. There are some locomotives whose maximum hp has been tuned close to 3900 hp and named as WDM-3A. They are still[when?] under production. WDM-3C is an upgraded loco from its previous WDM-3A. Their series is 14xxx.
This is the latest and the most advanced variant of all the available ALCOs. The WDM-3D are fitted with micro-processors. This variant has enhanced cabin facilities including left hand driving. This loco also has some features borrowed from its mate EMD GT46PAC. Features such as microprocessors to detect wheel slipping and phased manner power supply, monitoring engine parameters are incorporated from the latest EMD GT46PAC. This proved this variant a real success. Serial production began in 2005 and almost all diesel broad gauge sheds were allotted with this loco. The minor variants of this loco include WDM–3E and WDM–3F. They belong to series 11xxx.
WDG-3A, previously known as WDG-2 were designed owing to the problems which arose with WDM-2 on hauling freight. This loco normally hauls freight. The common problems were poor ride quality, lateral oscillations, and poor traction with heavy loads. First loco was manufactured in 1995. The gear ratio is 74:18. This loco has a balancing speed of 69 km/h with a load of 58 BOXN wagons (Max. speed 100 km/h). This variant is being gradually modernized to the level of WDM-3Ds. Some of its minor improvements include WDG-3B, WDG-3C and WDG-3D. Their series are in 14501-14999 and 13000-13665. Last one built for Indian Railway was 13665 rolled out in 2012. Total 1171 were built for Indian Railways and a considerable number were supplied to non Railway customers like thermal power plants, port trusts and steel plants 
The locomotive is used by the following zones of Indian Railways:
- South Western Railway
- Southern Railway
- Central Railway
- South Central Railway
- Northern Railway
- North Western Railway
- Northeast Frontier Railway
- West Central Railway
- East Central Railway
- Western Railway
- South East Central Railway
- East Coast Railway
- North Central Railway
- North Eastern Railway
- Eastern Railway
- South Eastern Railway