The Thompson A1/1 Pacific
Thompson initially worked on
producing a mixed-traffic Pacific,
before working on a new express passenger design.
With the intention of improving the A4
Thompson drew up two modified
Gresley 3-cylinder designs.
These designs discarded the conjugated gear and had separate sets of Walschaerts valve gear for each
Due to space restrictions, the middle cylinder could not be parallel with the outside cylinders.
One design had the middle cylinder forward of the outside cylinders, whilst the chosen design had
the middle cylinder further back. Both designs used
A1 (by then reclassified A10)
No. 4470 Great Northern
was selected for rebuilding. It is unfortunate that Great Northern (the very first
Gresley Pacific) was chosen for
this rebuilding, rather than being selected for future preservation.
There has been much debate on the reason for this choice. Some state it as bad luck, whilst others
Thompson for letting his
personal feelings towards
Gresley to cloud his judgement.
It is known that the Chief Draughtsman and a number of high up officials within the LNER unsuccessfully
tried to deter
Thompson from rebuilding this engine.
Thompson's new ideas were incorporated
into the new locomotive, and very little of the original was used in the rebuilding.
Initially, the design incorporated wing-type smoke deflectors of the type used on the
A2/2 Pacifics. These were not very
successful, so plans for large smoke deflectors were produced.
Although the rebuilt locomotive emerged in September 1945, it was not until December that the new
smoke deflectors would be fitted.
A new set of frames were built for the rebuild. These were similar to
A4 frames except for the wheel spacings
at the front. The resulting wheelbase was 38ft 5in, even longer than the
Originally, the plan was to rebuild all of the remaining
A10s but this never occurred.
There were also plans for streamlining, but these were never acted upon.
In October 1945, the order was given to construct sixteen new locomotives to the new A1/1 plan.
These finally appeared during
Peppercorn's tenure, by which
point the A1/1 design had evolved into the
Peppercorn A1 Pacific design.
Great Northern was actually officially designated Class A1 until 1947 when it was
reclassified Class A1/1 in anticipation of these new
Peppercorn A1 Pacifics.
In the first few years of service, the rebuilt Great Northern suffered a number of teething
problems. These were fixed, but it never played a prominent role on the East Coast Main Line.
Although it was occasionally allocated to Kings Cross, it spent much of its career based at
Doncaster or Grantham. Great Northern was even allocated to be the Grantham pilot for a while
during the mid-1950s.
Great Northern was renumbered No. 113 in
Thompson's 1946 renumbering scheme.
It then became No. 60113 during British Railways ownership, before being
withdrawn on 19th November 1962 with a badly worn middle cylinder.
Although usually remembered as a folly on
Thompson's part, it has to be remembered
that the A1/1 was a better locomotive than either the
A4 Pacifics before they were converted to
use Kylchap exhausts.
||1281.4 sq.ft. (121x 2.25in)
||1063.7 sq.ft. (43x 5.25in)
||(@ 85% boiler pressure)
||159 tons 8cwt
||101 tons 10cwt
||58 tons 18cwt
|Max. Axle Load:
Although No. 4470 Great Northern would have been an
ideal choice for preservation, this was not to be.
Rebuilt as Class A1/1, it was withdrawn in November 1962 with mechanical problems.
The late LBSC designed a 3.5" gauge locomotive called 'Hielan Lassie' that is a good representation of the
A1/1 without the smoke deflectors.
PDK Models produce a kit of the A1/1 for 4mm scale / OO gauge.
Thank you to the P.H. Groom collection for permission to use the above photograph of BR No. 60113 Great Northern
with large smoke deflectors.