The London and North Eastern Railway Class P1 Mineral 2-8-2 Mikado was a class of two steam locomotives designed by Nigel Gresley. They were two of the most powerful freight locomotives ever designed for a British railway. It was initially intended they be a more powerful 2-10-0 version of the earlier Class O2 2-8-0s. The design was submitted in August 1923, for use between Peterborough and London, and also between Immingham and Wath marshalling yard. The power was quoted as being 25% more than the O2. Construction and into service The first P1, No 2393, was completed by Doncaster in June 1925 and was shown at the Darlington Centenary celebrations in July, with its sister No 2394 following in November 1925. Both were externally rather similar, although 2393 had a 32-element superheater while 2394 had a larger 62-element 'E' type superheater. They were the first 2-8-2 locomotives to be built in Britain for local use, although not the first designed. Both were allocated to New England shed after completion where they were subjected to regular testing. In service, the P1s could handle 100-wagon coal trains, although these were an operational hazard due to their overhanging track circuits and being too long for many of the passing loops. They were also coal-hungry engines, with a 1926 Locomotive Inspectors Conference Report stating that the engines used of coal. However, they were still thought of highly enough in 1926 that it was proposed to build another four P1s to replace an equivalent number of 0-8-0s. The boosters The P1 class engines were initially equipped with two-cylinder booster engines attached to the trailing axle. They were engaged using a Westinghouse pump mounted on the boiler to engage the cylinder clutch. The booster engine had a tractive effort of when used, increasing the tractive effort of the locomotive from . It was intended by Gresley that these boosters would be used to assist the locomotive while starting, and in topping the banks over which they travelled. The tenders attached to the P1s had a specially-designed dragbox to accommodate the booster equipment. In practice, the boosters were troublesome. When in operation, they filled the cab with steam, and the fireman's workload was doubled. The steam pipes from the boiler to the booster were prone to fracture, particularly on the sharp curves of the turning triangle at the New England shed. The boosters were removed from engines