The LNER Class A4 is a class of streamlined 4-6-2 steam locomotives designed by Nigel Gresley for the London and North Eastern Railway in 1935. 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. Thirty-five of the class were built to haul express passenger trains on the East Coast Main Line route from London King's Cross via York to Newcastle, and later via Newcastle to Edinburgh. 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. At least six A4s saw out their remaining days until 1966 in Scotland, particularly on the Aberdeen – Glasgow express trains, for which they were used to improve the timing from 3.5 to 3 hours.
Overview Gresley introduced the Class A4 locomotives in 1935 to haul streamlined Silver Jubilee trains between London King's Cross and Newcastle. The service was named in celebration of the Silver Jubilee of George V.
During a visit to Germany in 1933, Gresley had been inspired by high-speed streamlined Flying Hamburger diesel trains. The London and North Eastern Railway (LNER) had considered purchasing similar trains for use from London to Newcastle but the diesel units of the time could not carry enough passengers and were too expensive. Gresley was sure that steam could do equally well with a decent fare-paying load behind the locomotive. Following trials in 1935 in which one of his A3 Pacifics, No. 2750 Papyrus, recorded a new maximum of 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. Initially four locomotives were built, all with the word 'silver' in their names. The first was 2509 Silver Link, followed by 2510 Quicksilver, 2511 Silver King and 2512 Silver Fox. During a press run to publicise the service, Silver Link twice achieved a speed of , breaking the British speed record, and sustained an average of over a distance of .
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.
Design The A4 Pacifics were designed for high-speed passenger services. 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. A further design improvement was fitting a Kylchap double-chimney, first on No. 4468 Mallard in March 1938. The double-chimney improved the capability of the locomotives further, and the last three locomotives of the class (4901 Capercaillie, 4902 Seagull and 4903 Peregrine) were fitted with the Kylchap exhaust from new and the rest of the class acquired it in the late 1950s.
The class was noted for its streamlined design, which not only improved its aerodynamics, increasing its speed capabilities, but also created an updraught to lift smoke away from the driver's line of vision, a problem inherent in many steam locomotives particularly those operated with short cut off valve events; fitting smoke deflectors was an alternative solution. The distinctive design made it a particularly attractive subject for artists, photographers and film-makers. The A4 Class locomotives were known by trainspotters as "streaks".
The streamlining side skirts (side 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. This apart, the A4 was one of few streamlined steam locomotive designs in the world to retain its casing throughout its existence. Many similar designs, including the contemporary Coronation Class, had their streamlining removed or cancelled to cut costs, simplify maintenance and increase driver visibility.
World record
On 3 July 1938, 4468 Mallard - the first of the class to enter service with the Kylchap exhaust - pulling six coaches and a dynamometer car, set a world speed record (indicated by the dynamometer) of . Gresley never accepted it as the record-breaking maximum. He claimed this speed could only have been attained over a few yards, though he was comfortable that the German speed record of had been surpassed. 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. 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. On the other hand, the German train was four coaches long (197 tons), but Mallard's train had seven coaches (240 tons). One fact, often ignored when considering rival claims, is that Gresley and the LNER had just one serious attempt at the record, which was far from a perfect run with a 15 mph permanent way check just north of Grantham; despite this a record was set. Gresley planned another attempt in September 1939, but was prevented by the outbreak of World War II. Prior to the record run on 3 July 1938, it was calculated that 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.
At the end of Mallards record run, the middle big end (part of the motion for the inside cylinder) ran hot (indicated by the bursting of a heat-sensitive "stink bomb" placed in the bearing for warning purposes), the bearing metal had melted and the locomotive had to stop at Peterborough rather than continue to London. Deficiencies in the alignment of the Gresley-Holcroft derived motion meant that the inside cylinder of the A4 did more work at high speed than the two outside cylinders – on at least one occasion this led to the middle big end wearing to such an extent that the increased piston travel knocked the ends off the middle cylinder – and this overloading was mostly responsible for the failure.
Performance in service No other British steam locomotives have a longer or more consistent record of high speed running than the A4s. Instances of 100 mph running by them must exceed those of all other types combined, though running was a relatively rare event with steam traction, much less . A4s operated on the East Coast Main Line which has more opportunities for high speed running (particularly Stoke Bank) than any other in the UK.
In August 1936, the Silver Jubilee train on the descent of Stoke Bank headed by No. 2512 Silver Fox driven by George Henry Haygreen achieved a maximum of , then the highest speed attained in Britain with an ordinary passenger train. The fastest recorded post-war speed with British steam was also recorded by an A4. This occurred on 23 May 1959 on the Stephenson Locomotive Society Golden Jubilee special when No. 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.
Although A4s were primarily designed for high speed express work they were also capable of high power outputs. 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 for . On W.A. Tuplin's method for grading steam locomotive performance based on both power output and duration of effort, this was the highest value ever achieved by any British locomotive, at Grade 26.
The highest recorded power output from an A4 was 2,450 drawbar horsepower when Mallard itself was hauling 11 coaches (390 tons tare, 415 tons gross) up Stoke Bank at a sustained in 1963. O. S. Nock thought this performance superior to Mallard's world record run in 1938. An A4 with the same load on a "good run" would be doing about at the summit of Stoke Bank. On a run on 8 September 1961 Mallard had its train travelling at .
Post-war history
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.
Even after the war was over, the A4s still continued to perform non-stop services. In August 1948, No. 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. It would hold this record until No. 4472 Flying Scotsman'''s visit to Australia in 1988.
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. 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.
The wholesale application of double Kylchap chimneys to the entire class was entirely due to the persistence of P.N. Townend, the Assistant Motive Power Superintendent at London King's Cross from 1956. He, at first, met with considerable resistance from higher authority. When permission was eventually given, it was found that the economy obtained over the single chimney A4s was from six to seven pounds of coal per mile, which more than justified the expense of the conversion.
These improvements led to greatly increased availability.
Locomotive data Original LNER number Final LNER number BR number Doncaster Works number Original name (rename(s)) Entered service Withdrawn Notes 2509 14 60014 1818 Silver Link 2510 15 60015 1819 Quicksilver 2511 16 60016 1821 Silver King 2512 17 60017 1823 Silver Fox 4482 23 60023 1847 Golden Eagle 4483(585) 24 60024 1848 Kingfisher 4484(586) 25 60025 1849 Falcon 4485(587) 26 60026 1850 Kestrel(Miles Beevor from November 1947) 4486(588) 27 60027 1851 Merlin 4487 28 60028 1852 Sea Eagle(Walter K. Whigham from October 1947) 4488 9 60009 1853 Union of South Africa(Osprey, its originally allocated name, during 1980s–90s due to opposition to apartheid) Preserved 4489 10 60010 1854 Woodcock(Dominion of Canada from June 1937) Preserved 4490 11 60011 1855 Empire of India 4491 12 60012 1856 Commonwealth of Australia 4492 13 60013 1857 Dominion of New Zealand 4493 29 60029 1858 Woodcock 4494 3 60003 1859 Osprey(Andrew K. McCosh from October 1942) 4495 30 60030 1860 Great Snipe(Golden Fleece from September 1937) 4496 8 60008 1861 Golden Shuttle(Dwight D. Eisenhower from September 1945) Preserved 4497 31 60031 1862 Golden Plover 4498 7 60007 1863 Sir Nigel Gresley Preserved 4462 4 60004 1864 Great Snipe(William Whitelaw from July 1941) 4463 18 60018 1865 Sparrow Hawk 4464 19 60019 1866 Bittern Preserved 4465 20 60020 1867 Guillemot 4466 6 60006 1868 Herring Gull(Sir Ralph Wedgwood from January 1944) 4467 21 60021 1869 Wild Swan 4468 22 60022 1870 Mallard Currently holds the world speed record for steam locomotives at , preserved 4469 – – 1871 Gadwall(Sir Ralph Wedgwood from March 1939) Damaged beyond repair by bomb on 29 April 1942. 4499 2 60002 1872 Pochard(Sir Murrough Wilson from April 1939) 4500 1 60001 1873 Garganey(Sir Ronald Matthews from March 1939) 4900 32 60032 1874 Gannet 4901 5 60005 1875 Capercaillie(Charles H. Newton from September 1942)(Sir Charles Newton from June 1943) 4902 33 60033 1876 Seagull 4903 34 60034 1877 Peregrine(Lord Faringdon from March 1948)