LNER Thompson Class A1/1

This article is about the locomotive in its rebuilt form. For the locomotive as it was originally built, see GNR Class A1 1470 Great Northern.

Not to be confused with LNER Class A1, LNER Class A1/A3, or LNER Peppercorn Class A1.

The LNER Class A1/1 consisted of a single 4-6-2 "Pacific" express passenger locomotive rebuilt in 1945 from an A1 class locomotive, by Edward Thompson. It was intended as the prototype of a new design of pacific locomotives improving the A4 design of Thompson's predecessor Sir Nigel Gresley. No further examples were built due to Thompson's retirement in 1946.

LNER Thompson Class A1/1
The single Thompson A1/1 Pacific 60113 Great Northern near Peterborough in 1959
Type and origin Power type Steam Designer Edward Thompson Build date 1922 Rebuilder Doncaster Works Rebuild date 1945 Number rebuilt 1
Specifications Configuration: ​  • Whyte 4-6-2  • UIC 2'C1' h3 Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 3 ft 2 in (0.965 m) Coupled dia. 6 ft 8 in (2.032 m) Trailing dia. 3 ft 8 in (1.118 m) Wheelbase 63 ft 6.625 in (19.37 m) ​  • Engine 38 ft 5 in (11.71 m)  • Coupled 14 ft 6 in (4.42 m) Length 73 ft 2 in (22.301 m) Loco weight 101.5 long tons (103.1 t; 113.7 short tons) Tender weight 60.7 long tons (61.7 t; 68.0 short tons) Total weight 159.5 long tons (162.1 t; 178.6 short tons) Fuel capacity 9 long tons (9.144 t) Water cap. 5,000 imp gal (22,730.45 L; 6,004.75 US gal) Firebox: ​  • Grate area 41.5 sq ft (3.86 m2) Boiler 6 ft 5 in (1.96 m) max diameter Boiler pressure 250 psi (1.72 MPa) Heating surface: ​  • Firebox 231.2 sq ft (21.48 m2)  • Tubes 1,281.4 sq ft (119.05 m2)  • Flues 1,063.7 sq ft (98.82 m2)  • Total surface 2,576.3 sq ft (239.35 m2) Superheater: ​  • Heating area 748.9 sq ft (69.58 m2) Cylinders Three Cylinder size 19 in × 26 in (483 mm × 660 mm) Valve gear Walschaerts Valve type Piston valves
Performance figures Tractive effort 37,400 lbf (166.36 kN)
Career Operators London and North Eastern Railway British Railways Class LNER: A1/1 Power class BR: 8P6F Numbers 4470/113/60113 Retired 1962 Disposition Scrapped

Background

When Edward Thompson was appointed Chief Mechanical Engineer of the London and North Eastern Railway in April 1941, he envisaged a new standardisation programme involving ten locomotive designs including two Pacific types. These were an express passenger type (designated A1) with 6 ft 8 in (2.032 m) driving wheels and a ‘heavy passenger and freight’ type (designated A2) with 6 ft 2 in (1.880 m) driving wheels. He was not able to proceed with his plan due to the Second World War but did try out some of his ideas by rebuilding Nigel Gresley’s P2 class 2-8-2 as A2/2 pacifics and building the last four V2 class already on order as A2/1 pacifics. At last in July 1944 Thompson began work on designing his new A1 class incorporating everything learned from the twenty-plus years of Gresley's development of the 6 ft 8 in (2.032 m) Pacific locomotives along with the construction and operation of the rebuilt P2 and A2/1. Thompson had no desire to rebuild the Gresley A10 and A3 classes to the new specification as he believed they were an essential part of the LNER locomotive fleet, with Simon A.C. Martin suggesting that O.S. Nock's pamphlet produced for the LNER may have suggested so. Some commentators believed that he intended to rebuild one of the surviving Gresley pacifics of the A1 class to try out the new design.

Design

Thompson's A1/1 design differed from his previous designs by adopting a divided drive with the centre cylinder, where the inside connecting rod was of a different length to the outside one, ignoring the presumed advantages provided by an equal length connecting rods and the subsequent valve events. This gave an elongated look with the resulting wheelbase being 38 ft 5 in (11.709 m) long, even longer than the Gresley P2s.

The final design omitted the inside Gresley conjugated valve gear in favour of three independent sets of Walschaerts valve gear. Steam was generated using a diagram No. 107 boiler, which was used on Gresley A4 locomotives, necessitating the use of A4 frames. The smokebox was carefully developed based on the practice set by the rebuilt P2 locomotives. Thompson followed Gresley's development with a double Kylchap chimney and his draughting arrangement. There was also a reversion to flat fronted cabs and cab floor out of safety concerns, similar in style to Gresley A3 and in dimension to his B1 locomotives. Electric lighting and hinged discs were fitted to the front of the locomotive.

Rebuilding

No. 4470 Great Northern, the very first Gresley Pacific, was chosen for this rebuilding rather than being retained for future preservation. There has been much debate on the reason for this choice. Some has blamed Thompson for letting his personal feelings towards Gresley cloud his judgement. O. S. Nock describes it as ‘the most disappointing and tactless act in his short and stormy career as CME,’ and C. J. Allen stated ‘he turned it into a machine of such hideous appearance as might well have made its designer turn in his grave.’

Simon A.C. Martin believes that Thompson lacked tact and has misread the attachment of the railwaymen to Great Northern and the selection of the locomotive was not his decision, but that of the Locomotive Running Superintendent. Such a decision would have been based on the proposed locomotive's age, total mileage to date, mileage since last shopping and overall condition. The late Richard Hardy, a draughtsman working on Great Northern stated that had the Chief Draughtsman Teddy Windle remonstrated with Thompson, Thompson would have replied that it was not his decision. As the first Gresley Pacific, Great Northern has been in service since 1922 and was being shopped at the time of the selection, hence its selection.

The A1 prototype was classed both as an express passenger locomotive and as a rebuild of an existing locomotive out of expediency due to wartime austerity measures. However, very limited amount of the original locomotive were retained in the rebuilding, such as the driving wheels, parts of the rear cartazzi, the tender frames and wheels. The boiler and original frame of the Gresley A10 were put into the spares pool with the frames refurbished and reused on another locomotive.

The rebuilt locomotive appeared in traffic in September 1945 in Great Eastern Railway Prussian Blue with double red lining with "NE" on the tender, likely in direct tribute to three of four major railways that made up the LNER, however no written reasoning, instruction or notice were given. The locomotive was classified A1 while the remaining sixteen locomotives of Gresley's A1 class were re-classified A10.

There were also plans for streamlining all the members of the new A1 class, but these were never acted upon, with a logical scenario being due to wartime austerity measures making the additional material requirement of streamlining unacceptable to the LNER Emergency Board.

New-build Class A1

In October 1945, the order was given to construct sixteen new locomotives to the new A1 plan. However, before these could be built Thompson had retired and Arthur Peppercorn had taken over as CME and he deferred building them until 1948, by which time he had altered the design to become the Peppercorn Class A1 Pacific design. In 1947 Great Northern, up to then the sole member of the class officially designated Class A1, was reclassified Class A1/1 in anticipation of these new Peppercorn A1s.

The A1/1 in service

The rebuilt locomotive had excellent steam generation due to utilising an A4 boiler and had a tractive effort of 37,400 lbf (166.36 kN), which made it one of the most powerful pacifics within the LNER, surpassing the Gresley A4 with only the A2/2 surpassing it. In the same year with only three working months, it achieved 22,052 mi (35,489.25 km) engine miles, compared to the A4 locomotives working in Scotland, which had the highest mileage that year and averaged 57,065 mi (91,837.22 km).

It then went on to become the highest mileage Pacific with an annual figure of 68,304 mi (109,924.63 km), outperforming the next best Gresley Pacific by around 15,000 mi (24,140.16 km). Engine report cards from the LNER archives at the National Railway Museum shows that Great Northern's rebuilt form achieved 55,882 mi (89,933.36 km) per year, matching Gresley A4s and Peppercorn A1s.

For the rest of its working life, Great Northern achieved significantly higher availability than other Pacific classes on the LNER, with its first working year, 1946, achieving 83%. This is partially due to the difference in maintenance approach between the Gresley locomotives, which were often run to failure, while Thompson Pacifics had preventative maintenance and desired high availability.

Renumbering

Great Northern was renumbered No. 113 under Thompson's 1946 renumbering scheme. It then became No. 60113 during British Railways ownership.

Withdrawal

60113 was withdrawn on 19 November 1962 with a badly worn cylinder and was then broken up at Doncaster Works. By the time of its withdrawal, Great Northern achieved the highest mileage out of all the Thompson Pacifics and was one of the best locomotives in terms of overall availability for work. An attempt to save the engine from being scrapped was unsuccessful.

Models

PDK Models produce a kit of the A1/1 for 4 mm scale / OO gauge.

References

• Allen, Cecil J. (1962). British Pacific Locomotives. London: Ian Allan.
• Nock, O.S. (1984). British Locomotives of the Twentieth Century Vol. 2 1930-1960. London: Book Club Associates.
• Boddy, M. G.; Neve, E.; Yeadon, W. B. (April 1973). Fry, E. V. (ed.). Locomotives of the L.N.E.R., Part 2A: Tender Engines—Classes A1 to A10. Kenilworth: RCTS. ISBN 0-901115-25-8.
• Yeadon, Willie (1991). Yeadon's Register of LNER Locomotives, Vol. 3: Raven, Thompson and Peppercorn Pacifics.
• Martin, Simon A.C. (2021). Edward Thompson: Wartime CME. Strathwood Publishing.
• Railway Mania (6 July 2019). "Edward Thompson, Hero or Villain? (with Simon A.C. Martin) - Railway Mania PODCAST #5" (Podcast). Retrieved 22 October 2022.

External links

• The Thompson A1/1 Pacific LNER Encyclopedia