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{{Infobox locomotive
| name = Indian locomotive class YP
| image = File:India - Railway Museum Mysore 62.jpg
| caption = No. 2511 on display at the Railway Museum, [[Mysore]].
| powertype = Steam
| builder = [[Baldwin Locomotive Works]] [[North British Locomotive Company]] [[Krauss-Maffei]] [[Tata Motors|Tata Engineering and Locomotive Co.]]
| builddate = 1949–1970
| totalproduction = 871
| whytetype = {{whyte|4-6-2}}
| uicclass = 2'C1'
| gauge = {{track gauge|1000 mm}}
| coupleddiameter = {{convert|1372|mm|ftin|abbr=on}}
| wheelbasewithtender = {{convert|16333|mm|ftin|abbr=on}}
| over buffers = {{convert|19088|mm|ftin|abbr=on}}
| width = {{convert|2590|mm|ftin|abbr=on}}
| height = {{convert|3430|mm|ftin|abbr=on}}
| axleload = {{convert|10.5|t|abbr=on}}
| serviceweight = {{convert|99|t|abbr=on}}
| fueltype = Coal
| fuelcap = {{convert|9.8|t|abbr=on}}
| watercap = {{convert|3000|gal|abbr=on}}
| firearea = {{convert|2.6|m2|sqft|abbr=on}}
| boilerpressure = {{convert|14.4|bar|psi|abbr=on}}
| tubesandflues = {{convert|134|m2|sqft|abbr=on}}
| totalsurface = {{convert|103.35|m2|sqft|abbr=on}}
| superheaterarea = {{convert|30.75|m2|sqft|abbr=on}}
| cylindercount = Two, outside
| cylindersize = {{convert|609|mm|in|abbr=on}}
| valvegear = [[Walschaerts valve gear|Walschaerts]]
| t/e starting = {{convert|82|kN|lbf|abbr=on}}
| operator = [[Indian Railways]]
| fleetnumbers = See [[#Table of builders and numbers|table]]
| notes = References (unless where noted): {{sfn|da Costa|1952|p=516}}
}}

The '''Indian locomotive class''' '''YP''' are a class of {{whyte|4-6-2}} [[Locomotive#Use|passenger]] locomotives built for [[Indian Railways]]' [[Metre-gauge railway|metre gauge]] network as one of several post-[[Partition of India|partition]] standard designs evolved from the pre-[[World War II|war]] Indian Railway Standard designs.<ref name="delPrado"/>

== History ==
The YP locomotives were intended to replace the earlier [[Indian locomotive class YB|YB]] and [[Indian locomotive class YC|YC]] class locomotives of the original IRS series designs.{{sfn|da Costa|1952|p=520}} A total of 871 locomotives were built between 1949 and 1970 by various manufacturers. They were among the most commonly used steam locomotives in the country and one of the last built specifically for passenger service in the world. [[Baldwin Locomotive Works]] delivered the first batch of 20 locomotives in 1949, followed by another 100 from the [[North British Locomotive Company]],<ref name="rg">{{cite magazine|date=14 November 1952|title="YP" Locomotives for India|url=https://archive.org/details/sim_railway-gazette-international_1952-11-14_97_20/page/550/mode/1up|volume=97|magazine=[[Railway Gazette International]]|location=|publisher=|pages=550, 553|access-date= 8 August 2025|via= [[Internet Archive]]}}</ref> with [[KraussMaffei|Krauss-Maffei]] supplying a further 200 locomotives between 1952 and 1954. The remaining 551 were domestically built by [[Tata Motors|Tata Engineering and Locomotive Co.]] between 1954 and 1970.<ref name="delPrado"/>{{Sfn|Hughes|1977|p=24}}

Until the 1990s, YP class were in service on India's metre-gauge network in large numbers, especially, in the states of [[Rajasthan]], [[Assam]] and [[Tamil Nadu]].<ref name="delPrado">{{cite book|author=|title=Information sheet for the YP class|publisher=Ediciones del Prado|location=Madrid|date=2005|ISBN=|page=2}}</ref>

Several examples have been preserved and are now on display in various locations in India. Numbers 2257 and 2684 were sold in 1990 to American-owned [[Railroad Development Corporation]] and were seen in [[Togo]] {{As of|2007|lc=y}}.<ref>{{cite web|access-date=2022-07-05 |title=Benin Tourist Railway Project |url=https://www.trevorheath.com/livesteaming/Benin-Togo.htm}}</ref>

== Table of builders and numbers ==
{| class="wikitable" style="text-align:center"
!Year
!Quantity
!Builder
!Serial number
!Running number
|-
|1949
|20
|[[Baldwin Locomotive Works]]
|74454–74473
| rowspan="4" |2000–2870 ''(not in order)''
|-
|1952
|100
|[[North British Locomotive Company]]
|27120–27219
|-
|1952–1954
|200
|[[KraussMaffei|Krauss-Maffei]]
|17732–17781, 17991–18140
|-
|1954–1970
|551
|[[Tata Motors|Tata Engineering and Locomotive Co.]]
|51–150, 201–290, 761–830, 845–935, 956–1155
|-
|}

== Design ==
As the replacement for the original IRS design YB class, which had less efficient steaming from the coal which they were fired on with the lower grate area of the class,{{sfn|da Costa|1952|p=520}} and for the YC class, which were barred from working lighter lines due to their heavy axle load,{{sfn|da Costa|1952|p=520}} the superheating and upgraded valve gear of the YPs made them more powerful than the YBs and YCs.{{sfn|da Costa|1952|p=520}}

The YPs were greatly standardised between the [[Indian locomotive class YG|YG]] class locomotives, which were their [[Rail freight transport|goods]] counterparts.{{sfn|da Costa|1952|p=517}} Many parts of both classes were shared with each other.{{sfn|da Costa|1952|p=517}} Moreover, both locomotives shared the designs of parts from their broad-gauge counterparts, the [[Indian locomotive class WG|WG class]] and the [[Indian locomotive class WP|WP class]], scaled down from their broad gauge versions, allowing common maintenance procedures.{{sfn|da Costa|1952|p=517}}

Since the locomotives were intended for use on routes with relatively low axle loads, they had to be as light as possible. For this reason, the {{Clarify span|side panels|Smoke deflectors?|date=November 2024}} and cab were made of aluminum as a weight-saving measure.<ref name="delPrado"/>

== Allocation ==
The YP class locomotives were used all over India. By the end of 1976, the locomotives were allocated to the following regional zones of [[Indian Railways]]:{{Sfn|Hughes|1977|p=96}}
{| class="wikitable" style="text-align:center"
!Zone
!Quantity
|- style="text-align:right"
| style="text-align:left" |[[Central Railway zone|Central Railways]]
|9
|- style="text-align:right"
| style="text-align:left" |[[Northern Railway zone|Northern Railways]]
|101
|- style="text-align:right"
| style="text-align:left" |[[North Eastern Railway zone|North Eastern Railways]]
|235
|- style="text-align:right"
| style="text-align:left" |Northern Frontier Railway
|98
|- style="text-align:right"
| style="text-align:left" |[[Western Railway zone|Western Railways]]
|155
|- style="text-align:right"
| style="text-align:left" |[[South Central Railway zone|South Central Railways]]
|72
|- style="text-align:right"
| style="text-align:left" |[[Southern Railway zone|Southern Railways]]
|199
|-
|}
Two locomotives of this class had been withdrawn at the time.

== References ==
<references />
=== Bibliography ===
* {{cite magazine|last=da Costa|first=R. G.|date=14 November 1952|title=Metre-Gauge Locomotives for India|url=https://archive.org/details/sim_railway-gazette-international_1952-11-07_97_19/page/516/mode/2up|volume=97|magazine=[[Railway Gazette International]]|location=|publisher=|pages=516-20|access-date= 5 August 2025|via= [[Internet Archive]]}}
* {{Cite book |last=Hughes |first=Hugh |title=Steam Locomotives in India, Part 2 - Meter Gauge |date=1977 |publisher=The Continental Railway Circle |isbn=0-9503469-3-4}}
* {{cite magazine|date=7 November 1952|title="YP" Locomotives for India|url=https://archive.org/details/sim_railway-gazette-international_1952-11-14_97_20/page/550/mode/1up|volume=97|magazine=[[Railway Gazette International]]|location=|publisher=|pages=550, 553|access-date= 8 August 2025|via= [[Internet Archive]]}}

==Further reading==

* Brian Hollingsworth: ''Dampflokomotiven: Ein technisches Handbuch der bedeutendsten internationalen Personenzuglokomotiven von 1820 bis heute.'' Springer-Verlag, 1983, {{ISBN|978-3-7643-1530-6}}, YP class on p. 192

==External links==
* [https://www.irfca.org/gallery/Diagrams/INDIA-YP_20Diagram.jpg.html YP class diagram, Indian Railways Fan Club (IRFCA) website]

{{commons category|Indian locomotive class YP}}
{{Metre gauge locomotives of India}}

[[Category:Baldwin locomotives]]
[[Category:4-6-2 locomotives]]
[[Category:Steam locomotives of India|YP]]
[[Category:NBL locomotives]]
[[Category:Krauss-Maffei locomotives]]
[[Category:Railway locomotives introduced in 1949]]
[[Category:Metre-gauge steam locomotives]]
[[Category:Passenger locomotives]]
[[Category:2′C1′ h2 locomotives]]

Indian locomotive class YP - Revision history

Tirucochi: added info - done