LNWR Precursor Tank Class

{{Use dmy dates|date=April 2017}}

{{Use British English|date=April 2017}}

{{Infobox locomotive

| name = LNWR Precursor Tank

| powertype = Steam

| image = LNWR locomotive No. 528 Precursor Tank.jpg

| alt =

| caption = No. 528 in photographic grey livery

| designer = George Whale

| builder =

| ordernumber =

| serialnumber = 4560–4599,
4820–4829

| buildmodel =

| builddate = 1906–1909

| totalproduction = 50

| rebuilder =

| rebuilddate =

| numberrebuilt =

| whytetype = 4-4-2T

| uicclass = 2′B1 2t

| gauge = {{track gauge|ussg}}

| leadingdiameter = First 30: {{convert|3|ft|9|in|m|3|abbr=on}}
Last 20: {{convert|3|ft|3|in|m|3|abbr=on}}

| driverdiameter = {{convert|6|ft|3|in|m|3|abbr=on}}

| trailingdiameter = First 30: {{convert|3|ft|9|in|m|3|abbr=on}}
Last 20: {{convert|3|ft|3|in|m|3|abbr=on}}

| minimumcurve =

| wheelbase =

| length =

| width =

| height =

| axleload =

| weightondrivers =

| locoweight = {{long ton|74|15}}

| fueltype =

| fuelcap =

| watercap =

| sandcap =

| boiler =

| boilerpressure = {{convert|175|psi|MPa|2|abbr=on}}

| feedwaterheater =

| firearea =

| tubearea =

| fluearea =

| tubesandflues =

| fireboxarea =

| totalsurface = {{convert|1939|sqft|m2|abbr=on}}{{cite book |author=LNWR |date=December 1908 |title=Wages and Hours Arbitration |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hn5uml&view=1up&seq=38 |location=London |publisher=London and North Western Railway |page=334 |via=HathiTrust}}

| superheatertype =

| superheaterarea =

| cylindercount = Two, inside

| cylindersize = {{convert|19|x|26|in|mm|0|abbr=on}}

| valvegear = Joy

| valvetype =

| valvetravel =

| valvelap =

| valvelead =

| transmission =

| maxspeed =

| poweroutput =

| tractiveeffort = {{convert|15216|lbf|kN|2|abbr=on}}

| factorofadhesion =

| trainheating =

| locobrakes =

| locobrakeforce =

| trainbrakes =

| safety =

| operator = LNWR » LMS

| operatorclass =

| powerclass = LMS: 2P

| numinclass =

| fleetnumbers =

| officialname =

| nicknames =

| axleloadclass =

| locale =

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| firstrundate =

| lastrundate =

| withdrawndate = 1927–1940

| scrapdate =

| disposition = All scrapped

| notes =

}}

The London and North Western Railway (LNWR) "Precursor Tank" Class was a type of 4-4-2 tank steam locomotive.{{cite magazine |author= |date=23 September 1910 |title=Passenger Tank Engines. No. V |url=https://archive.org/details/sim_engineer_july-december-1910_110/page/336/mode/1up |magazine=The Engineer |volume=110 |pages=336–337 |via=Internet Archive}} Fifty were built to the design of George Whale between May 1906 and April 1909, being a tank engine version of his "Precursor" Class.{{cite book |last=Baxter |first=Bertram |date=1979 |editor-last=Baxter |editor-first=David |title=British Locomotive Catalogue 1825–1923, Volume 2B: London and North Western Railway and its constituent companies |location=Ashbourne |publisher=Moorland Publishing Company |isbn=0903485842 |pages=264–265}}

Chronologically, the class was constructed three distinct blocks, from May to September 1906 (works nos. 4560–4589), March to April 1907 (4590–4599), and March to April 1909 (4820–4829). The first 30 locomotives had {{convert|3|ft|9|in|m|3|abbr=on}} carrying wheels, but the size of these was reduced to {{convert|3|ft|3|in|m|3|abbr=on}} thereafter.

The LNWR reused numbers from withdrawn locomotives, so the numbering system was completely haphazard. The 3 ft 9 in engines were numbered by 528, 531, 784, 1295, 1305, 1981–1985, 97, 111, 181, 196, 562, 616, 803, 1356, 1508, 2210, 139, 653, 834, 874, 1506, 1572, 1589, 1671, 1714, and 2165. The 3 ft 3 in engines were numbered 44, 527, 612, 762, 827, 875, 1427, 1764, 2196, 2446, 920, 935, 1164, 1219, 1523, 1536, 1551, 2077, 2223 and 2228.

All fifty passed into LMS ownership in 1923. The LMS gave them the power classification 2P. The LMS also renumbered them into solid block of numbers: 6780–6809 for the 3 ft 9 in engines and 6810–6829 for the 3 ft 3 in engines, in the order given above.

Due to their weight, the Precursor Tanks were unable to operate on some branch lines, but had primarily been designed for use on heavy suburban trains.{{cite book |last=Montagu |first=George |date=1907 |title=Ten Years of Locomotive Progress |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hb4dz5&view=1up&seq=175 |location=London |publisher=Alston Rivers Ltd. |page=137 |via=HathiTrust}}{{cite magazine |author= |date=10 December 1921 |title=The "Precursor Tank" Locomotives of the London and North-western Railway |url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112088589822&view=1up&seq=569 |url-access=limited |magazine=The Locomotive News and Railway Notes |volume=10 |number=67 |pages=137–138 |via=HathiTrust}} Initially, they were put to work on local services between Sutton Coldfield and Birmingham, and also between Watford and London {{rws|Euston}}.{{sfnp|LNWR|1908|p=32}} In 1921, they were reported as being employed on the latter to the near-total exclusion of other locomotive types, as well as on other routes. 1572, which was possibly one of the earliest locomotives to have the initials "L&NWR" on its sides replaced by "LMS", was noted to be working on the Morecambe branch in 1923.{{cite magazine |last=Stones |first=H. R. |date=1923 |title=[untitled] |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015075068703&view=1up&seq=442 |url-access=limited |magazine=The Railway Magazine |volume=52 |issue=311 |page=428 |via=HathiTrust}}

One member of the class was withdrawn in October 1927, and the others between December 1931 and February 1940. None were preserved.