Their streamlined design gave them high-speed capability as well as making them instantly recognisable, and one of the class, 4468 Mallard, holds the record as the world's fastest steam locomotive.

They remained in service on the East Coast Main Line until the early 1960s when they were replaced by Deltic diesel locomotives; they themselves proving to be worthy successors to the A4s.

Gresley introduced the Class A4 locomotives in 1935 to haul streamlined Silver Jubilee trains between London King's Cross and Newcastle.

2750 Papyrus, recorded a new maximum of 108 mph (173.8 km/h) and completed the journey in under four hours, the LNER's Chief General Manager Ralph Wedgwood authorised Gresley to produce a streamlined development of the A3.

[4] Following the commercial success of the Silver Jubilee train, other streamlined services were introduced: The Coronation (London-Edinburgh, July 1937) and the West Riding Limited (Bradford & Leeds-London & return, November 1937) for which more A4s were built.

The application of internal streamlining to the steam circuit, higher boiler pressure and the extension of the firebox to form a combustion chamber all contributed to a more efficient locomotive than the A3; consumption of coal and water were reduced.

The streamlining side skirts (valances) designed by Oliver Bulleid to aerofoil shape that were fitted to all the A4 locomotives, were removed during the Second World War to improve access to the valve gear for maintenance and were not replaced.

Many similar designs, including the contemporary Coronation Class, had their streamlining removed or cancelled to cut costs, simplify maintenance and increase driver visibility.

[7] Close analysis of the dynamometer roll (currently at the NRM) of the record run confirms that Mallard's speed did in fact exceed that of the German BR 05 002.

[8]: 64  The Mallard record reached its maximum speed on a downhill run and failed technically in due course, whereas 05 002's journey was on level grade and the engine did not yet seem to be at its limit.

[10]: 126  Prior to the record run on 3 July 1938, it was calculated that 130 mph (210 km/h) was possible; Driver Duddington and LNER Inspector Sid Jenkins both said they might well have achieved this figure had they not had to slow for the Essendine junctions.

This occurred on 23 May 1959 on the Stephenson Locomotive Society Golden Jubilee special when 60007 Sir Nigel Gresley achieved 112 mph when hauling 400 tons down Stoke Bank.

The driver, Bill Hoole, had hoped for an attempt to beat Mallard's record but Alan Pegler, who was on the footplate and mindful of the risks, told him to ease off.

In 1940, 4901 Capercaillie exerted 2,200 drawbar horsepower on the straight and level track north of York when hauling 21 coaches (730 tons gross) at an average of 75.9 mph for 25 miles.

[16] Although newer Pacifics had been introduced since the war and the streamlined trains were never reinstated, the A4s continued on top link duties, notably on the London to Edinburgh services.

In August 1948, 60028 Walter K. Whigham managed to perform a non-stop service run from King's Cross to Edinburgh, setting the record for distance travelled for 408.65 miles.

[17] Improved methods of aligning the Gresley conjugated valve gear in the 1950s led to tighter tolerances for the bearings used within it and, consequently, to almost total eradication of the overloading of the middle cylinder.

[citation needed] History repeated itself with the inside big end being replaced by one of the Great Western type, after which there was no more trouble, provided that maintenance routines were respected.

One locomotive was withdrawn and scrapped after being damaged beyond repair in a German bombing raid on York on 29 April 1942 during World War II; this was No.

Both North American-based A4s, along with the other three British-based A4s were moved to the National Railway Museum, York, in late 2012 on three-year loans as part of the NRM's 2013 celebrations of the 75th anniversary of Mallard breaking the world speed record for steam, bringing all six preserved A4s together.