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The Gresley A0 Pacific Locomotive

& the Origins of the
North Western Railway's number 4

Written by Simon Alexander Martin & Sean O'Connor

For over a year I have made a study into the designs of Sir Nigel Gresley, unearthing some surprising facts about his line of 3-cylinder Pacific designs, and particularly, those designs he did not build.

At the same time, both using research made available by others, and my own into Gordon's origins as stated in the books The Island of Sodor (TIOS) and Reading Between the Lines(RBTL), I have collaborated on a unified theory with Sean O'Connor. We feel that we can finally shed light on Gordon's true origins, as a result of this collaborative effort.

But first, we must establish that we know to be fact, from our research into the ex-Great Northern Railway (GNR) and London and North Eastern Railway (LNER) designs in the early days of Sir Nigel Gresley's reign as Chief Mechanical Engineer (CME) of both companies whilst also speculating as to a legitimate fictional reality, on Awdry's behalf.

Simon Alexander Martin

The A0 Pacific Design of 1915

In 1915 for the then Great Northern Railway, Herbert Nigel Gresley, CME, would begin drafting plans for the locomotive that is seen in the picture below. This design would be described as an "extended Ivatt Atlantic", and certainly in styling, would be a reasonable approximation.

Drawing courtesy of the National Railway Museum, York.

This is the Gresley design which was believed for many years, to be the final drafted Pacific design before the emergence of the first production A1 Pacific, Great Northern. Outwardly the two designs appear to share little in common other than the number of wheels in a Pacific arrangement. Or do they?

It is our shared belief that this design was not merely tossed away by Gresley, only to start on a Pacific design from scratch. This locomotive, which we have christened for the purposes of this essay the “A0 Pacific”, can in some respects be thought as the first stepping stone, which directly led to the famous Gresley A1 pacific locomotive, of which class member no.4472 Flying Scotsman is the sole survivor.

According to the dimensions on the scaled drawings of its frames, the locomotive is identical in wheelbase to the later A1 Pacific locomotives: both its overall length, and its wheel spacings for the same 6ft 8in driving wheels are the same.

Based on the knowledge we have of Gresley's locomotive development at the time, we can speculate as to the technical information of the "A0 Pacific" if it had been built. With a wheelbase extremely similar to the that of the A1 Pacifics which emerged later, and the same 6ft 8in driving wheels and cartazzi arrangement, the A0 Pacific would have been "underboilered" when built. In this respect, we mean that the locomotive's boiler – in many respects, simply a stretched version of the Ivatt Atlantic from which it was derived – would not be as effective as the 180lb boiler which was designed for the A1 Pacific.

Technical Information

A0 Pacific — As Built

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A0 Pacific — "As Rebuilt by Gresley"

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Based on that we know of the original specification, and that which followed as the A1 Pacific, we can legitimately speculate that in the real world, Gresley and his design team re-used their work in the design of the frames of the A0, and its wheelbase, in his A1 Pacific locomotive.

Why? When the plans for the first A1 were revealed in 1922, we speculate that several parts of the A0 design were carried forward - frames, wheel spacing and driver size plus the use of three cylinders. We believe so because a crucial aspect of this design - the identical frames - can in theory carry the the larger Gresley Taper boiler so fitted to the A1 Pacific Great Northern, in real life.

Secondly, with a Gresley outline cartazzi truck, and different front end arrangement, the A0 drawing is in some respects halfway to the design development which would culminate in no.4470 Great Northern.

Between the completion of these locomotive drawings in 1915, and the out shopping of the first K3 mogul in 1920, Gresley had been to America and studied an American K4 locomotive. In the development of the K3, we see Gresley's use of the three cylinder front end arrangement.

The A0 design is a four cylinder locomotive: but the possibility of it being re-drawn as a three cylinder design is thought provoking. This is mere speculation of course: the two locomotive designs, A0 and A1, share little above the running plate, but that below the running plate – the frames and wheelbase - being so similar would be nothing short of remarkable coincidence.

What was puzzling when researching the development of the Pacific design, was that the design was not drafted in 1915 to include Gresley's "new" conjugated valve gear (actually based on a lapsed patent by the locomotive engineer Holscroft), however his experiments with a few Ivatt Atlantics and then the K3 suggest that he would not have included the three cylinder design until he was happy with its mechanics.

The locomotive which would be built - Great Northern - carried forward once more a logical progression with the fitting of a Gresley taper boiler, Gresley style cab and differently styled running plate. This was unique to the K3 and the 02 locomotives at this point, which shared the running plate and three cylinder development, but would not have their cabs rebuilt for some years to Gresley's improved design.

Thus, the A0 drawing can be considered more of a stepping stone to the A1 design than would otherwise have been seen. The same wheelbase, with identical spacing throughout, and the use of some distinctive traits later seen on the A1 Pacific tend to give credence, in Awdry's universe, to the A0 and Gordon being one and the same.

Gordon the A0 Pacific

Now for Gordon's true origins - the fictional side of the A0 Pacific locomotive story. We believe he is in fact the A0 design, albeit rebuilt and modified to a mechanically identical, but outwardly unique, locomotive. The description of Gordon in TIOS is clear:

“He was built at Doncaster as an experimental prototype for Mr Nigel Gresley's 4-6-2 Pacific for the Great Northern Railway. Inevitably there were faults that needed correction so Gordon was kept hush hush and apart from test runs was never put into regular traffic or given a GNR number. He was used experimentally till all defects had been cured and the first batch of Pacifics had appeared in 1922/23. In 1923 therefore Gordon was no longer needed and was sold to the NWR along with a spare boiler and firebox.”

Logically these are the facts we must take from the TIOS description of Gordon:

  • Gordon had to be the prototype for the A1 Pacifics.

  • He cannot be an existing locomotive like Great Northern, because he was never given a stock number or put into active traffic.

  • He was a work in progress and had all defects cured, then the A1s were drawn up and built off the knowledge gained through his building and trials.

  • He was sold as soon as the A1s were put into service, and therefore was not an active A1 Pacific.

In TIOS, it is stated that Gordon was "an experimental prototype for Mr Nigel Gresley's 4-6-2 for the Great Northern Railway". The A0 is an experimental design, which through research by Gresley was developed further to create a working Pacific design.

Gordon was "used experimentally until all defects had been cured and the first batch of Pacifics had appeared in 1922/23". The design was updated and redrafted to include developments that Gresley had experimented with, including attributes such as three cylinder propulsion and cartazzi arrangement. The design, A0 matches the description of Gordon here, and in RBTL, if we decide that this prototype was originally built by Gresley (thus fulfilling the requirements for Gordon's emergence).

The design uses what are essentially A1 frames and at least internally, once all defects had been cured could even be identical to an A1 mechanically. The only real differences are in the boiler and sylinder arrangement, which as stated earlier could in theory - and as we think in fiction - could have been exchanged for the full A1 taper boiler and a 3 cylinder arrangement later on. Gresley would have made the loco look less functional and more "form" once it had been in operation and he was satisfied with its progress.

Couple that with the fact that we have no illustrations of Gordon (as built circa 1920-1923) in the books to go against or contradict. This is far too likely to be Gordon, as it fits in with real life: this "hush hush" locomotive that we can feasibly could never have heard about, which in fiction was sold to the NWR and unlike the Great Northern theories, it doesn't alter real history.

Furthermore, the same design can be easily rebuilt into Gordon 2 (Gordon's NWR development) in the same fashion as a stock Gresley A1 because the core components - the frames and wheelbase - are the same. The rest, bar the obvious, necessary, and perfectly legitimate changes (boiler and cylinder arrangement), such as the cab and running plate arrangement, are trivial and aesthetic.

This can be in real life described as the stepping stone to the A1 Pacific design, and in fiction, if built in Awdry's universe, the prototype for the A1 class. With Gordon being described only as the prototype for the A1 class, there are (realistically speaking) no other options which tie into both reality and fiction like the A0 Pacific design does.

Furthermore, there is evidence that Gordon was intended by Wilbert Awdry to be a very different looking machine, albeit familiar if we have been looking closely at this Gresley design:

Awdry's vision: Note the similarities between Awdry's own hand drawn vision of
Gordon and the original A0 plans. Picture courtesy TRLOTTTE.

Pictured above is the earliest known sketch of Gordon, from the 1940s, in the form we believe Wilbert Awdry intended. This picture embodies the design aesthetics of the original A0 design quite remarkably.

It was originally thought that Wilbert Awdry could not have known that much about the A0 design - however...the design is chronicled in several books from the 1930s, and particularly in Cecil J.Allen's British Pacific Locomotive Design (an edition which was first written in the early forties and continuously updated until publication in the late sixties). Therefore, given the Reverend's love of reading, research and railways, it is not unthinkable that this design — which has the potential to be more than it seems on paper — would be the reverend's inspiration for the fictional character Gordon.

We have been able to produce some comparative pictures based on what we know, and Gordon's intended development. Components shared by the A0 and A1 — wheelbase and wheel spacing, plus driving wheels - have been used in the production of these mock-ups, as well as fitting the Gresley Taper boiler that, from the dimensions given to us in the drawings, we know will fit the design:

Picture attributed to Sean O'Connor.

Notice that the engine when fitted with a taper boiler looks remarkably A1 straight away — the only features different, are those aesthetic (and thus, easily changed parts of the design): the running plate and cab.

With this in mind, by the time Gordon as the sole A0 Pacific was no longer required, he would have gained the three cylinder arrangement, and taper boiler, and possibly other modifications such as the curved running plate at fore and aft (a Gresley trait which featured on his prototype 02 locomotive, found here on the LNER Encyclopedia Forum.

As stated in TIOS, Gordon was sold to the NWR for an undisclosed amount when he was no longer needed because the LNER had their A1s in service: they had no need for the prototype and never intended to put it into service. The LNER provided a spare boiler and firebox in the sale and the locomotive gave a good service until the valve gear as is typical to the type, started to give many problems. The exact nature of these problems is uncertain, but it is commonly thought to be some sort of catastrophic failure, probably at speed which lead to Gordon's subsequent...and rather unique rebuild in 1935.


With dedicated research, careful observation and working through the logical development of a real, factual design, we believe that Gordon's origins lie, not in the supposed relocation of the first Gresley production A1 (Great Northern) but in the use of a never built prototype, that through its re-drafts, and its original design legacy, did figure in the design development of the A1 Pacific for which Sir Nigel Gresley is rightfully remembered for, and here, Gordon the Big Engine who is remembered as being the class' prototype in fiction. By tying Gordon down to a real life design, with such logical development of point, we feel we can state that the A0 Pacific design of 1915 is Gordon as the Reverend W.Awdry intended in his book The Island of Sodor.


Allen, Cecil J, British Pacific Locomotives (London: Ian Allen Ltd, 3rd Edition 1990, originally published 1962).

Allen, Cecil J, Locomotive Practice and Performance in the Twentieth Century (Cambridge: W. Heffer & Sons Ltd, 2nd edition 1950).

Awdry, Christopher, Sodor: Reading Betwen the Lines (Oundle: Sodor Enterprises, 2005).

Awdry, Rev. Wilbert; Awdry, George, The Island of Sodor - Its People, History and Railways (London: Kaye and Ward, 1987).

Glover, Graham, British Locomotive Design (London: George Allen and Unwin Ltd, 1967).


Special Thanks and Acknowledgements

We wish to express our thanks and acknowledgements to the National Railway Museum, York, for the use of the technical drawings from their archives.

We would like to thank in particular the NRM's former Curator of Railway Vehicles, Jim Rees, for his help in the research stage, and wish him well at Beamish.

We would also like to thank the following people for their helpful critiques and support: Ryan Hagan, and Gavin Rose.

We'd like to thank in particular Martin Clutterbuck for hosting our research on his wonderful site. Thanks Martin!

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