|Origin of the Peppercorn class A1s|
In 1948 and 1949, the newly nationalised British Railways built, at its Doncaster and Darlington works, forty-nine class A1 Pacifics to the design of the LNER's last Chief Mechanical Engineer, Arthur Peppercorn.
In September 1945 Peppercorn’s predecessor, Edward Thompson, unveiled his rebuild of Gresley’s first pacific, 4470 Great Northern at Doncaster Works. It wasn’t just the engine’s new Royal blue livery lined out in red that was striking: very little remained of the original locomotive. The new Great Northern was an angular and ungainly looking locomotive. In spite of its well documented flaws, Thompson was sufficiently satisfied with his A1 to place an order for 16 new-build versions in October 1945 and then another 23 the following year.
However, these were the locomotives that three years later would emerge as the Peppercorn A1s, further modified from Thompson’s design. The first, 60114, appeared from Doncaster in August 1948 and was named W.P. Allen that October. Another 48 followed by the end of the following year, the last of the class being 60162 Saint Johnstoun.
The earlier Gresley pacifics, the most famous of which are class A3 4472 Flying Scotsman and class A4 4468 Mallard, were three-cylinder machines which drove all cylinders onto the middle axle. Peppercorn, like Thompson used divided drive, with the middle cylinder connected to the leading axle. Gresley had used conjugated valve gear, while Thompson and Peppercorn used three sets of Walschaerts. But, unlike Thompson, Peppercorn used a markedly larger grate, of 50 sq. ft - the same as that first used by Gresley on his magnificent class P2 2001 Cock O' the North. Most visibly the outside cylinders were back in their more conventional place resulting in a much more aesthetically pleasing locomotive and one much less prone to frame fractures. In fact JF Harrison went on to say in his presidential address to the Institution of Locomotive Engineers in 1961 that this was the kind of locomotive Sir Nigel Gresley would have designed had he still been alive.