LNER Class P2

The Edinburgh–Aberdeen main line was one of the LNER's most operationally challenging routes. Between Stonehaven and Aberdeen the line climbs steeply at 1-in-100 ruling gradients, and the principal expresses (the Aberdonian, the Granite City, the Saint Mungo) loaded heavily throughout the year. Existing A1 and A3 Pacifics could just about manage the route but were close to their limits, particularly in winter conditions when steam losses to gradient-induced heavy working were severe.

Sir Nigel Gresley's answer was the P2, a three-cylinder 2-8-2 Mikado for express passenger work. The eight-coupled wheel arrangement gave substantially more adhesion than a Pacific (six-coupled), making the engine ideally suited to the gradient-bound Aberdeen route; the wide Belpaire firebox supported by the trailing axle gave the necessary boiler capacity for the heavy expresses; and the 220 psi boiler pressure (against the A1's 180 psi) gave the additional power.

The first engine, No. 2001 Cock o' the North, emerged from Doncaster Works in May 1934. Gresley specified an experimental Lentz oscillating-cam valve gear for the prototype, an attempt to evaluate Continental practice that was sufficiently problematic in service that 2001 was reverted to standard Gresley conjugated gear in 1938. The engine was sent to France for high-speed and gradient testing in late 1934 and early 1935; the French test results showed that the P2's steam circuit was substantially below the GWR-derived best-practice standards used by Continental railways, and contributed to design improvements in the subsequent production batch.

2002–2006 followed in 1936, with the standard Gresley conjugated valve gear from new and minor design improvements informed by the 2001 trials. From 1937 onwards 2001 was rebuilt with a streamlined casing matching the A4 Class, although this was reversed in 1942 because of war-condition fouling on the casing. The class worked the Aberdeen route with distinction throughout the late 1930s and into the war years.

The P2s worked the principal Edinburgh–Aberdeen expresses through the late 1930s and the early war years. In service the class was widely admired for its capability on the heavy gradient-bound route. Performance was not without difficulties, the eight-coupled wheel arrangement on tight curves caused extra wear on the leading coupled flanges and required careful track maintenance, but on the Aberdeen route the class was in its element.

Edward Thompson succeeded Gresley as LNER CME on the latter's death in April 1941. Thompson took a fundamentally different view of locomotive policy, preferring two-cylinder simplicity and standardisation over Gresley's three-cylinder express designs, and from 1943 onwards he initiated the controversial rebuilding of the P2 class to two-cylinder Pacific form. All six P2s were rebuilt as A2/2 4-6-2 between 1943 and 1944, with the eight-coupled drive replaced by six-coupled drive and the original three-cylinder layout replaced by two cylinders.

The Thompson rebuilds were strongly criticised by the LNER preservation community both at the time and since, the rebuilds eliminated the unique 2-8-2 design that Gresley had specifically tailored for the Aberdeen route, and produced a class of A2/2 Pacifics that were widely considered inferior to the original P2s on their intended duty. The rebuilt engines continued in BR service (renumbered 60501–60506) on the Edinburgh–Aberdeen and East Coast main-line work until 1961.

None of the original P2s survived in their original form, the Thompson rebuilds extinguished the class as built. The rebuilt A2/2 Pacifics were all withdrawn between 1959 and 1961, with no examples preserved.

The P2 was the largest British express locomotive of its era, a three-cylinder 2-8-2 Mikado with eight-coupled drive and a wide firebox. The original 2001 Cock o' the North was distinguished from the production engines by its experimental Lentz oscillating-cam valve gear (later reverted to standard Gresley conjugated gear) and by the rounded German-style smoke-deflector and chimney that gave the prototype a distinctive Continental appearance. The production engines (2002 onwards) had the standard Gresley appearance with conventional smoke-deflectors. From 1937 onwards 2001 was rebuilt with a streamlined casing matching the A4 Class, although the modification was reversed in 1942. The class wore LNER apple green with Hopkins-pattern lining and brass nameplates carrying the Scottish names.

2001 Cock o' the North, first of class, completed at Doncaster in May 1934 with experimental Lentz oscillating-cam valve gear. The engine's distinctive German-style smoke-deflectors and the celebrated Scottish name made it one of the most photographed British locomotives of the 1930s. Trialled in France in 1934–1935 (where French testing showed the engine's steam circuit was below GWR-derived best practice). Rebuilt with streamlined casing 1937; reverted to standard appearance 1942. Rebuilt to A2/2 form by Thompson in 1944. Withdrawn from BR service in 1959.

2007, a new-build P2 No. 2007 Prince of Wales currently under construction by the A1 Steam Locomotive Trust (the same team that built the new-build Tornado). The engine takes the next-in-series number 2007 (the original sequence having ended at 2006). Construction has been ongoing since 2014; the engine is partly assembled but is at the time of writing not yet operational. The choice of Prince of Wales as the name reflects the Patron of the project.

LNER service (1934–1944): the entire class was concentrated on Haymarket (Edinburgh) and Ferryhill (Aberdeen) sheds for the Edinburgh–Aberdeen main-line expresses. The class worked the Aberdonian, the Granite City, the Saint Mungo and the Bon Accord, the principal northbound expresses out of Edinburgh and the southbound expresses out of Aberdeen. The route's 1-in-100 ruling gradients between Stonehaven and Aberdeen, and the substantial passenger loadings throughout the year, made the P2's exceptional tractive effort particularly valuable.

Post-rebuild as A2/2 (1944–1961): all six engines were rebuilt to A2/2 4-6-2 Pacific form by Edward Thompson between 1943 and 1944. In rebuilt form the class was widely distributed across the Eastern Region, King's Cross, Doncaster, Heaton (Newcastle), and continued in BR service to 1961.

LNER (1934–1947, P2 form): LNER apple green with Hopkins-pattern lining, polished brass nameplates carrying the Scottish names, and the LNER coat of arms or "L.N.E.R." lettering on the tender. 2001 wore experimental finishes including a streamlined casing 1937–1942.

Post-rebuild A2/2 (1944–1961): initially LNER apple green; then BR Brunswick green from 1949 with the early lion-and-wheel emblem and later late BR crest.