LNER high pressure compound No. 10,000 ‘Hush-Hush’

© Phil Copleston

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London & North Eastern Railway Class W1 four-cylinder compound No. 10,000 known as the “Hush-Hush” loco, photographed in the early 1930s.

Designed by that railway’s Chief Mechanical Engineer, Nigel Gresley, as an experimental steam locomotive, its purpose was to test the railway use of high-pressure steam water-tube boilers then in vogue in marine applications. It was completed at the LNER’s Darlington Works in 1929 and had a 4-6-4 wheel arrangement; the only tender loco of this type to run on a British railway.

The locomotive was never officially named. Plans in 1929 to name it “British Enterprise” were dropped, although nameplates had already been cast. It was popularly known by the nickname “Hush-Hush” however, due to the secrecy surrounding its development. Railwaymen, of course, knew it more scurrilously as the “Galloping Sausage” because of its bulging shape!

Now some technical details: The unique water-tube boiler, with a working pressure of 450psi (3.10MPa), was built by Glasgow shipyard boilermakers Yarrow & Company who had experience in this type of pressure vessel in marine applications. Underneath the streamlined cladding, the boiler resembled two elongated marine boilers joined end to end. This had a triangular arrangement of a central steam drum above two separated water drums, linked by multiple rows of slightly curving tubes. This gave the ‘boiler’ an overall triangular but curved cross-section. Longitudinally, the lower edge of each section stepped upwards, as was obvious in the locomotive’s external appearance.

Here is a drawing of the locomotive’s internal arrangement:

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Fitted with Walschaerts valve gear, the two inside high pressure cylinders were 12 x 26 inches (305mm x 660mm) bore and stroke, and the two outside low-pressure cylinders 20 x 26 inches (508mm x 660mm) bore and stroke. The driving wheels were 6ft 8ins (2.032m) diameter. Tractive effort was 32,000 pounds (142.3kN).

In service, the locomotive was fitted with a corridor tender (to enable crew changes) and used on the high profile non-stop London to Edinburgh services, including the prestige “Flying Scotsman” express. Nevertheless, steaming was relatively poor during test and service runs, and despite modifications to exhaust, the boiler never reached the standards of an equivalent firetube boiler. Consequently, in 1936 after six years use it was rebuilt with a conventional modified A4 class-type boiler and fitted with three simple expansion cylinders, but retained its 4-6-4 wheel arrangement and continued in regular service with the LNER.

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Liveries: From new No. 10,000 was painted in an unusual dark battleship grey livery with steel clothing bands and 12ins (304mm) high numbers on the cab sides and lettering on the tender in white with black shading. Rather spiffing! During the war years it was painted a sombre black, later garter blue after the war in 1946. Under nationalised British Railways ownership it was renumbered 60700 and painted a darker blue in January 1951, then a mid-green from May 1952.

In June 1959, No. 60700 was withdrawn and later broken up at Doncaster Works. Remarkably, the tender that ran with the “Hush Hush” survives today in preservation behind streamlined A4 Class 4-6-2 “Union of South Africa”. Thus, in part, the spirit of this unusual experimental locomotive lives on!

Video: You can see a short film of the “Hush Hush” here,shot in 1930 when new: http://www.britishpathe.com/video/l-n-e-r-s-lner-hush-hush-engine

Further reading: “Hush Hush: The story of LNER 10000” byWilliam Brown (Kestrel Railway Books, July 2010, ISBN 1 905505 15 9) A locomotive monograph based largely on original papers housed at the National Railway Museum, York.

Heading photo: This photo is from an enhanced digital image in my collection.

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