The LMS referred to 10000 as Britain's first mainline diesel locomotive. Prior to 10000 many shunters were trialled across the UK but only one 'large' diesel locomotive is known to have been trialled on the UK mainline. Armstrong Whitworth trialled a 1-Co-1 diesel electric locomotive on the LNER in 1933. The power unit used was an Armstrong-Sulzer 8LD28 with eight cylinders inline. The rated output was 800hp at 700rpm.
This locomotive had been designed for mixed traffic use with a maximum axle loading of 17 tons, a maximum tractive effort of 28,500lb. Its maximum speed of 70mph and it was permitted to haul 800 ton freights or 260 ton passenger trains.
The locomotive entered service on the LNER on July 6th 1933, it worked a small number of trial trains. It was an experimental undertaking and the LNER did not take interest in it since they were having great success with steam power at that time. The loco was withdrawn from service in June 1934 after crankcase failure.
Although sometimes referred to as the first mainline diesel in the UK the Armstrong Whitworth loco should correctly be referred to as the first diesel locomotive to be trialled on the mainline. In comparison, 10000 was both constructed by a mainline railway company and ran extensively in public service between 1948 and 1963. It was one of 5 pioneer locomotives which successfully trialled the new diesel technology and led the way to many first generation classes notably 40 and 50 which shared the same basic 16SVT and 16CSVT design power units. Classes 31 and 37 has 12 cylinder versions of the engine.
Photo courtesy Armstrong Whitworth Diesel Railway Traction
Narrow gauge diesel locomotives were used in World War 1 on military railways, however it was not until the 1930s before standard gauge railways employed experimental diesel power. At that time diesels were limited in terms of power output and so their application was limited. All four mainline railway companies experimented to some degree with diesel shunters. It was the LMS railway which extensively pursued a fleet of shunters, which led eventually to the standard class 08/09.
Photo: LMS loco 1831, Derby Works, 1932
Little appears to have been recorded about this locomotive which ran tests on the G.E. section of the LNER in 1924. It was a diesel-hydraulic 0-4-0 built by the Graz Works in Austria. Some sources list this as being built by Simmerung-Graz-Pauker, but other sources list this company as only coming into existence in the 1940s. It appears to have been their first diesel locomotive. Although it was a small locomotive, better suited for shunting duties, trials included main line haulage of four passenger coaches between London and Cambridge in August or September 1924.
Photo: Unknown. Article credit: https://www.lner.info/locos/Experimental/Graz040.php
Meanwhile various methods of economising on the costs of local rail services were tried, from steam powered railmotors to electric multiple units. The GWR produced railcars which successfully led to the first generation of Diesel Multiple Units in the 1950s.
Derby Sulzers website: Armstrong Whitworth locomotive (derbysulzers.com) Railway Matters (PDF): https://derbysulzers.com/aw.html
Early BR Main Line Diesels https://railwaymatters.files.wordpress.com/2021/02/early-br-main-line-diesels.pdf