The prototype was built by American Locomotive Company (ALCO) for the Northern Pacific Railway (NP) in 1926, with a very large firebox with a 100-square-foot (9.3 m2) grate, designed to burn low quality lignite coal.

[1] The 4-8-4 type arrived when nearly all the important steam locomotive design improvements had already been proven, including Superheaters, mechanical stokers, outside valve gear and the Delta trailing truck.

The increased boiler size possible with this type, together with the high axle loads permitted on mainlines in North America, resulted in the design of some massive locomotives, some of which weighed as much as 450 tons, including the tender.

Scaled down examples of the type were exported by two American builders, ALCO and Baldwin Locomotive Works, for 1,000 mm (3 ft 3+3⁄8 in) metre gauge lines in Brazil.

In a later variant, Bowen added a booster to the trailing truck, enabling the Selkirk to exert nearly 50% more tractive effort than the similar-sized K-1a Northern.

When it was demonstrated that a three-unit EMD F3 diesel-electric consist that weighed slightly less than the total engine and tender mass of a CPR K-1a Northern could produce nearly three times its tractive effort, high-powered steam locomotives were retired as quickly as finance allowed.

The booster contributed an additional 8,000 pounds-force (36 kilonewtons) to the tractive effort and permitted an increase in the locomotive's load across the Mount Lofty Ranges to 540 tons.

Although work was halted due to the outbreak of the Second World War, a shortage of motive power caused by increased wartime traffic resulted in authorisation being given for the completion of class leader H220.

[6] After his retirement from the Société nationale des chemins de fer français (SNCF) in France, French engineer André Chapelon was appointed as the chief designer of 1,000 mm (3 ft 3+3⁄8 in) metre gauge 4-8-4 locomotives at the French state-owned sales consortium Groupement d'exportation de locomotives en Sud-Amérique (GELSA).

The Belpaire firebox included a combustion chamber and the boiler pressure was a high 18 standard atmospheres (1,800 kilopascals; 260 pounds per square inch).

[9][10] In 1936, the German builder Henschel & Son supplied ten 5 ft 6 in (1,676 mm) gauge 4-8-4 locomotives to the Ferrocarriles del Estado (State Railways or FdE) of Chile, designated the Tipo 100.

[11] In 1933, the Beijing–Hankou Railway in China needed new locomotives for their Guangzhou to Shaoguan line, where gradients of around two percent, curves with less than 250 metres (820 feet) radius and low capacity bridges existed.

When the Changsha–Guangzhou Railway was completed in October 1936, the locomotives were transferred to operate over the northern section between Hankou and Changsha on this new mainline, which connected Guangzhou with Tianjin and Beijing.

[14][15][16] The lone prototype, numbered 242A1, of the Société Nationale des Chemins de fer Français (SNCF) was one of the five known classes of three-cylinder 4-8-4 locomotives.

[19][20] After the construction of thirty K class locomotives, the NZR developed the design to strengthen the frame and introduced other improvements, such as roller bearings on all axles and ACFI (Accessoires pour les Chemins de Fer et l'Industrie) feedwater heaters.

The streamlining shrouds of the KA and KB classes were removed in the late 1940s when the ACFI feedwater heaters were replaced with exhaust steam injectors.

One-third of the total length of the tender was taken up by the water tank and coal bunker, while the rest was taken up by eight large radiators on each side, cooled by five steam-driven roof-mounted fans.

Roller bearings were used throughout on all these locomotives, including the coupling and connecting rods, the crosshead gudgeon pins as well as the three-axle bogies of both the standard and condensing tenders.

[23] However, the Class 25 was a complex locomotive that required high maintenance, especially on the turbine blower fans in the smokebox, whose blades needed to be replaced frequently due to damage by solid particles in the exhaust.

The rebuilding took place at the Salt River shops of the SAR in Cape Town and was based on the principles developed by Argentinian mechanical engineer Livio Dante Porta.

The primary objectives of the modifications were to improve the combustion and steaming rate to reduce the emission of wasteful black smoke and to overcome the problem of clinkering.

[citation needed] Later, when electrification and dieselisation expanded, many of the Class P36 locomotives were transferred to work on the Lviv, Far East, Eastern Siberia, and Transbaikal Railways.

[citation needed] The 242F class express passenger 4-8-4 locomotives were designed by the Red Nacional de los Ferrocarriles Españoles (RENFE) in 1955 and were remarkably well-proportioned.

They had Witte type smoke deflectors and were fitted with a double KylChap (Kylälä-Chapelon) blast-pipe, a Worthington feedwater heater and a Traitement Integral Armand (TIA) water-softening device.

To increase the comfort of the locomotive crew, the cabs had wooden floors mounted on springs, and the seats of the driver and fireman were also sprung, a very welcome improvement for long runs on poor tracks.

For example, for the 163-kilometre long (101-mile) stretch between Medina del Campo and Burgos that rises 131 metres (430 feet) with an uphill start, three intermediate stops, one slack and some shunting movements to couple extra coaches to the train, the amount of water consumed was about 7,300 imperial gallons (33,000 litres).

[citation needed] All ten locomotives were allocated to the Miranda de Ebro shed to haul principal heavy express trains.

War intervened and suspended development of express passenger locomotives, but the 4-8-4 design was re-examined in 1942 by Fairburn, the acting CME, as a possible post-war type for fast fitted freights.

The lightest 4-8-4s in the United States were the six H-10 class locomotives of the Toledo, Peoria and Western (TPW), with an axle load of 23 short tons (21 tonnes).

Between 1945 and 1947, the Reading Railroad rebuilt thirty of their heavy I-10 class 2-8-0 Consolidations to booster-fitted 4-8-4 Northern locomotives with 70 inches (1,778 millimetres) diameter driving wheels.