One of this country’s largest classes of locomotives, numbering almost 500 strong, was the product of a private company. Not only was it a large class numerically but also physically; for at the time of their inception these saddle tank locomotives were the biggest in "private" use.
Unlike many industrial locomotives their construction was announced publicly, but the wartime cloak of secrecy did not reveal any details. In September 1943 the "Railway Magazine" announced that the "Ministry of Supply has recently placed orders with locomotive manufacturing firms in this country for a number of 0-6-0 saddle tank engines to a simple and robust design based by the Ministry on a standard shunter of a well known locomotive building firm". This well known firm was the Hunslet Engine Co. Ltd.
The well known firm was the Hunslet Engine Co. Ltd., of Leeds, established in 1854, and the standard shunter was their 18in by 26in cylinder "50550" class. Externally the "new" locomotive was almost identical to the earlier ones, with the exception of the cab and bunker outline. Cab roofs at the eaves were now radiused and bunkers were extended beyond the rear buffer beam, having a vertical end as opposed to the former sloping back; this gave a 5 cwt increase in coal capacity. There were other differences not readily discernible, the majority being internal changes in construction. Driving wheels were now 4ft 3in diameter as against 4ft 0½in and had cast iron centres; steel boiler tubes were substituted for brass, and phosphor bronze replaced the white metal for the coupling rod bushes. The locomotive scaled almost 2 tons more than the original but the tractive effort decreased from 26280 lbs to 23870 lbs, the boiler pressure remaining the same at 170lbs per sq. in. Steam brakes were fitted to all wheels and could be operated from either side of the cab. Valve gear was Stephenson link motion and slide valves were fitted to the 18in by 26in cylinders.
It is unfortunate that the word "Austerity" was applied to them, but at the time this was the "with-it" way of describing almost anything adapted to the stringent wartime simplification of production. Their illustrious record proves that even the pruning of the original super-quality specification did no harm.
Many thanks to http://www.irsociety.co.uk/Archives/23/18in_Hunslets.htm
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