Purists will call it
semi-streamline, but in 1929 its curved shrouding seemed revolutionary. It was built three years before the
Flying Hamburger, five years before the
Commodore Vanderbilt
and has a distinction of being the direct predecessor of LNER A4 Class -
the fastest steam locomotives on the face of the Earth!
The experimental Gresley W1 No. 10000 "Hush-Hush" was the only 4-6-4 tender locomotive to run in Britain*.
It included a number of experimental features including a marine type
water-tube boiler working at 450psi. Although this original design is
usually dismissed as a failure due to the revolutionary water-tube
boiler, No. 10000 did successfully work a number of high profile trains.
It never carried a name, although it was often referred to as the
"Hush-Hush" due to the initial secrecy of the project.
At the end of 1924, the American Locomotive Co. (Alco) Works at
Schenectady produced the world's first main line locomotive with a
high-pressure water-tube boiler. This was a 2-8-0 goods locomotive
called No. 1400
Horatio Allen,
which was built for the Delaware & Hudson. This used two-cylinder
compound expansion, and had a 350psi boiler. Due to the similarity with
marine practice, the Clyde shipbuilders of Yarrow & Co. were
consultants to Alco on this project. Development of the W1 also started
in 1924, when
Nigel Gresley
was considering ways of efficiently generating steam which used less
coal than the (then) heavy coal consumption of the A1 Pacifics.
In
September 1924, Gresley approached Harold Yarrow (of Yarrow & Co.),
and over the next three years they designed a new water-tube boiler for
locomotive use. The resulting water-tube boiler consisted of a long
steam drum, and four water drums. The water drums were connected to the
steam drum with a series of tubes through which water circulated (see
photograph):
Gresley's earliest design using a water-tube boiler was from April 1926,
and was for a 4-6-2 express passenger locomotive. This was intended to
be comparable to the A1 Pacifics, and would have had three-cylinder
compound working. This design would have had no space on the footplate
for the crew. It was quickly modified by shortening the front of the
boiler, and moving the furnace forward. Cylinder sizes were changed, and
a fourth cylinder was added. Darlington recommended replacing the
trailing wheels with a two-axle bogie, but this was not immediately
acted upon. By 1927, the boiler pressure had been increased from 350psi
to 450psi, and the requirement for the low-pressure cylinders was
reduced to 200psi. On seeing an outline drawing in June 1927 which
showed excessive rear over-hang and heavy loading on the trailing axle,
Gresley instructed Darlington to change the wheel arrangement to 4-6-4.
Technically, the rear bogie was partially articulated, with the first
axle in an A1-style trailing axle but with restricted movement, and the
rear axle was a true pony truck. Hence, many claim the W1 was
technically a 4-6-2-2, rather than a Hudson (Baltic) 4-6-4.
With the addition of the extra axle, Yarrow recommended that the
firegrate was extended. Initially Gresley added 7.5in, but this was
removed due to concerns about footplate size. Fitting a water-tube
boiler into the restrictive British loading gauge was proving a problem.
Orders for the cylinders were placed in July 1928, along with the first
parts of the Yarrow boiler. Although an official announcement of the
"Hush-Hush" was still a month away, news of a mysterious new locomotive
began to leak out of Doncaster Works. By February 1929, the boiler had
been constructed and fitted to the smokebox. Simultaneously, Professor
W.E.Dalby conducted a series of wind tunnel experiments which resulted
in the unusual front end. This required some changes to the smokebox
design. The boiler tests were completed by October 1929, and the
partially-assembled locomotive was shipped to Darlington. To maintain
secrecy, shipping over LMS lines required the locomotive to be sheeted
up.
The locomotive was completed in November 1929, and first ran on 12th
December. It then experienced six months of trials (including
modifications), before entering traffic.
After further tests, No. 10000 "Hush-Hush" entered service on 20th June
1930. It reached the 70,000 mile mark in May 1933, and it entered
Darlington Works for its first general repair. The opportunity was used
to apply further modifications. The blastpipe orifice was reduced from
4.75in to 4.25in, and its height lowered by 2.5in. Condensation in the
low-pressure cylinders was a problem whilst the engine was standing.
Chapelon recommended that the exhaust from the high-pressure cylinders
should be re-superheated before being reused in the low-pressure
cylinders. Gresley accepted this recommendation, and fitted an
intermediate superheater of 153sq.ft. This added about 100F to the
temperature of the low-pressure steam.
Other modifications made at this time included the addition of aluminium
foil insulation between the boiler and the casing; and the addition of
circulation tubes connecting the front and rear water drums of the
boiler. The locomotive returned to service in June 1934.
W1 No. 10000 ('Hush-Hush') entered Darlington Works again on 21st August
1935 for further repairs, having run about 90,000 miles since new. A
number of further modifications were being considered, when Gresley
ordered all further work to stop whilst he considered a scheme to
rebuild it with a conventional fire-tube boiler.
On 13th October 1936, the water-tube boiler W1 made its last journey:
from Darlington Works to Doncaster Works to be rebuilt with a
conventional fire-tube boiler. Out of the 1,888 days since it was built,
No. 10000 spent 1,105 days in Darlington Works.
No. 10000 was moved to Doncaster for rebuilding on 13th October 1936. An
outline design based on an A1 pattern boiler stretched to proportions
similar to P2/2 Wolf of Badenoch was produced by 24th November 1936.
This design had three 20in cylinders, a boiler pressure of 250psi, and
A4-style streamlining. When No. 10000 finally emerged from Doncaster in
November 1937, it closely resembled this outline plan.
As much as possible of the original locomotive was kept, including the
frames which had to be shortened by 18in. The trailing wheel arrangement
was left unchanged.
No. 10000 retained its number under the Thompson 1943 renumbering
scheme, but was renumbered to No. 60700 under the British Railways
renumbering scheme of 1948.
After a problematic career, the lone W1 was finally withdrawn on 1st June 1959.