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Mallard at the National Railway Museum, York

Number 4468 Mallard is a London and North Eastern Railway Class A4 4-6-2 Pacific steam locomotive built at Doncaster in 1938.

The Mallard was designed by Sir Nigel Gresley as an express locomotive. Its wind-tunnel-tested, aerodynamic body allowed it to reach speeds of over 100 mph (160 km/h). Mallard was released into traffic for the first time on March 3rd 1938. She was the first A4 to be fitted with a Kylchap double blast pipe from new. This was one of the features that would shortly select her for the attempt on the world rail speed record in the following July.

Mallard was in service until 1963, when she was retired, having covered almost one and a half million miles (2.4 million km).

She was restored to working order in the 1980s, but has not operated since, apart from hauling some specials between York and Scarborough in July 1986 and a couple of runs between York and Harrogate/Leeds around Easter 1987. Mallard is the only surviving A4 in LNER livery and in as-built original condition with side valances (although the valances are replicas).

Mallard is now part of the National Collection at the National Railway Museum in York.

The locomotive is 70 ft long and weighs 165 tons, including the tender. It is painted LNER garter blue with red wheels and steel rims.

Mallard is the holder of the world speed record for steam locomotives at 126 mph (202.7 km/h). The record was achieved on July 3, 1938 on the slight downwards grade of Stoke Bank south of Grantham on the East Coast Main Line, and the highest speed was recorded at milepost 90¼, between Little Bytham and Essendine. It broke the German (DRG Class 05) 002's 1936 record of 124 mph (200.4 km/h).

Mallard was the perfect vehicle for such an endeavour; one of the A4 class of streamlined locomotives designed for sustained 100+ mph (160 km/h) running, it was one of a small number equipped with a double chimney and double Kylchap blast-pipe, which made for improved draughting and better exhaust flow at speed. The A4's three-cylinder design made for stability at speed, and the large 6 ft 8 in (2.032 m) driving wheels meant that the maximum revolutions per minute was within the capabilities of the technology of the day. Mallard was five months old, meaning that it was sufficiently run-in to run freely, but not overly worn. Selected to crew the locomotive on its record attempt were driver Joseph Duddington (a man renowned within the LNER for taking calculated risks) and fireman Thomas Bray.

The locomotive had had problems with the middle big end previously, so a "stink bomb" of aniseed oil was placed inside the big end, that would be released if it overheated. Shortly after the attainment of this record speed, Mallard suffered an overheated inside big end bearing and had to limp back to Peterborough after setting the record, it then travelled to Doncaster for repair. This had been foreseen by the publicity department, who had many pictures taken for the press, in case Mallard did not make it back to Kings Cross.

The Ivatt Atlantic that replaced Mallard at Peterborough was only just in sight when the head of publicity started handing out the pictures. Inaccuracies in the machining and setup of the Gresley-Holcroft derived motion (which derived the valve motion of the inside cylinder from those of the other two, avoiding a hard-to-maintain valve gear linkage between the frames) meant that the inside cylinder of the A4 did more work at high speed than the two outside cylinders; this overloading was mostly responsible for the failure.

Mallard wore a variety of liveries throughout her career, these were: garter blue as 4468, LNER wartime black from June 13th 1942, later wartime black with the tender marked as "NE" from October 21st 1943 as 22 with yellow small stencilled numbers, post-war garter blue with white and red lining from March 5th 1948 with stainless steel cab-side number 22, British railways dark blue as 60022 from September 16th 1949, Brunswick green from July 4th 1952 and regaining her original LNER garter blue for preservation in 1963.

As with all 35 of the Gresley A4 pacific steam locomotives, Mallard was fitted with streamline valances, or side skirting, when she was built. This was found to hinder maintenance and, like her sisters, it was removed. 4468 lost her valances during a works visit on June 13th 1942, regaining them in preservation in 1963.

Mallard was fitted with twelve boilers during her 25 year career. These boilers were: 9024 (from construction), 8959 (from 4496 Golden Shuttle, June 13th 1942), 8907 (from 2511 Silver King, August 1st 1946), 8948 (from 31 Golden Plover, March 5th 1948), 8957 (from 60009 Union of South Africa, September 16th 1949), 29282 (from 60028 Walter K Whigham, January 10th 1951), 29301 (from 60019 Bittern, July 4th 1952), 29315 (from 60014 Silver Link, April 23rd 1954), 29328 (new-build boiler, June 7th 1957), 29308 (from 60008 Dwight D. Eisenhower, August 27th 1958), 29310 (from 60009 Union of South Africa, March 9th 1960) and 27965 (from 60009 Union of South Africa, August 10th 1961).

Mallard has had seven tenders throughout her career. She started off with a non-corridor tender in 1938, had corridor-tenders during her British Railways days and was fitted with a non-corridor tender in 1963 to recreate her original appearance. The tenders she has been fitted with are: 5642 (March 3rd 1938 - March 14th 1939), 5639 (May 5th 1939 - January 16th 1948), 5323 (March 5th 1948 - March 12th 1953), 5648 (March 12th 1953 - July 21st 1958), 5330 (August 27th 1958 - May 30th 1962), 5651 (May 30th 1962 - April 25th 1963) and 5670 (current tender, masquerading as original tender 5642).

Mallard was allocated to three sheds during her career: Doncaster, Grantham (transferring October 21st 1943) and Kings Cross ('Top Shed'), transferring on April 11th 1948.

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