The Thompson O1 2-8-0 Locomotives

Thompson O1 No. 63752 at Annesley in 1958 (M.Peirson)

Thompson became the LNER's CME in 1941, and quickly initiated a programme of standardisation. One of Thompson's first standardised designs was for a heavy goods 2-8-0 to replace all of the existing 2-8-0s, 0-8-0s, and a variety of 0-6-0s including the J19s, J20s, J38s, and J39s. Wartime restrictions made the construction of new locomotives difficult, so Thompson chose to create his new O1 class by rebuilding the numerically large O4 'ROD' locomotives. The original design used the B1 boiler and cylinders, Walschaerts valve gear, L1 pony truck, 9in-shorter frames, side-window cab, and a Group Standard 4,200 gallon tender. This design was amended slightly by the time the first O1 was built. The boiler pressure was increased slightly from 220psi to 225psi, and a straight running plate ran from just ahead of the cylinders back to the cab. The maximum axle load was also increased. For economic reasons, the original O4 pony truck and tender were kept, and the frames were not shortened.

Rebuilding started in February 1944 with No. 6595, and operated in parallel with the O4/8 rebuild programme. The condition of the locomotive, especially the cylinders and valve gear, determined the choice of rebuild. The O1 rebuilds were included in the LNER's post-war modernisation programme, but slowed due to the LNER's immediate need for heavy goods locomotives being met by Stanier 8F (O6) and Riddles WD (O7) locomotives. The rebuild programme finally ended in 1949 after a post-Nationalisation review of rebuild programmes. A total of 58 O4 locomotives were rebuilt as O1s.

The cylinders were of the standard B1 type, 20in diameter with a 26in stroke. They were inclined at 1-in-50 and fitted with 10in diameter piston valves. The drive was to the third of the driving axles. The new cylinders represented a reduction in diameter, but this was compensated for by an increase in boiler pressure.

Gravity-fed sanders were fitted ahead of the first and third coupled axles for forward running. An extra pair of sanders were fitted behind the fourth coupled axle, for reverse running.

The first O1s were put through an extended series of trials throughout the LNER network. By the end of 1946, the forty of the class were allocated to Gorton, with much smaller numbers allocated to March, Tyne Dock, and Thornton. The Gorton engines were used over the Woodhead route, whilst the March locomotives mainly worked freight traffic from Whitemoor to Temple Mills.

The Thompson O1s were chosen for the British Railway Interchange Trials in 1948. These trials showed the design to be good but suffered from poor maintenance. The original GC (Great Central) side rods also tended not to work well with the Walschaerts valve gear, and their boilers suffered the same firebox problems as the B1s.

Allocations changed quite a bit with Nationalisation (1948). By 1951, Tyne Dock's allocation stood at five, and the remaining 53 Class O1s were allocated to Annesley. Due to the poor water quality present in the Annesley area, these locomotives had their tenders fitted for water treatment. A cylindrical container was fitted in the tender's water tank, and chemical briquettes were dropped into the container. These chemicals reduced scaling in the boiler tubes. The 'scale' either remained in suspension, or accumulated at the bottom of the boiler as a sludge. A blow down valve was then fitted in the lower part of the boiler, so that the sludge could be removed. The five Tyne Dock engines were also fitted with these valves by 1956.

In 1952, the five Tyne Dock engines were fitted with two 10in diameter Westinghouse pumps to operate the iron ore block trains from Tyne Dock to Consett. These trains ran with specially build hoppers that used compressed air to operate their hopper doors. The trains were also vacuum braked, so a vacuum ejector was also fitted.

During the 1960s, March received an allocation of O1s to work south to Temple Mills.

Withdrawals started in 1962, and were completed by 1965. The last O1s to be withdrawn were from Staveley shed. The Thompson O1s were outlived by three classes that they were intended to replace (J38, O4, and Q6).

Technical Details

The following details describe the original Thompson O1 locomotives. From November 1945, the number of boiler tubes was reduced from 143 to 141. This resulted in a reduction of the tube heating surface to 1033 sq.ft., and a reduction in the total heating surface from 2020 sq.ft. to 2005 sq.ft.

Cylinders (x2): 20x26in.
Motion: Outside: Walschaerts
Valves: 10" piston
Boiler: Max. Diameter: 5ft 6in
Pressure: 225psi
Diagram No.: 100A
Heating Surface: Total: 2020 sq.ft.
Firebox: 168 sq.ft.
Tubes: 1048 sq.ft. (143x 2in)
Flues: 460 sq.ft. (24x 5.25in)
Superheater: 344 sq.ft. (24x 1.244in)
Grate Area: 27.9 sq.ft.
Wheels: Leading: 3ft 6in
Coupled: 4ft 8in
Tractive Effort: (@ 85% boiler pressure) 35,518lb
Wheelbase: Total: 51ft 2.5in
Engine: 25ft 5in
Tender: 13ft 0in
Weight (full): Total: 121 tons 12cwt
Engine: 73 tons 6cwt
Tender: 48 tons 6cwt
Max. Axle Load: 17 tons


None of the Thompson O1s survived into preservation.


Hornby produce a ready to run model of the Thompson O1 in OO gauge (4mm scale) model.


Thank you to Malcolm Peirson for the photograph of BR No. 63752.