Under the Whyte notation for the classification of steam locomotives, 4-6-4 represents the wheel arrangement of four leading wheels on two axles, usually in a leading truck, six powered and coupled driving wheels on three axles, and four trailing wheels on two axles, usually in a trailing truck. In France, where the type was first used, it is known as the Baltic, while it became known as the Hudson in most of North America.
Other equivalent classifications are:
- UIC classification: 2C2 (also known as German classification and Italian classification)
- French classification: 232
- Turkish classification: 37
- Swiss classification: 3/7
- Russian classification: 2-3-2
Tender locomotives 
The 4-6-4 tender locomotive was first introduced in 1911 and throughout the 1920s to 1940s the wheel arrangement was widely used in North America and to a lesser extent in the rest of the world. The type combines the basic design principles of the 4-6-2 Pacific type with an improved boiler and larger firebox that necessitated additional support at the rear of the locomotive. In general, the available tractive effort differed little from that of the Pacific, but the steam-raising ability was increased, giving more power at speed. The 4-6-4 was best suited to high-speed running across flat terrain. Since the type has fewer driving wheels than carrying wheels, a smaller percentage of the locomotive's weight contributes to traction, compared to other types. Like the Pacific, it was well suited for high speed passenger trains, but for starting heavy freight trains and slogging on long sustained grades, more pairs of driving wheels are better.
The first 4-6-4 tender locomotive in the world was a four-cylinder compound locomotive, designed by Gaston du Bousquet for the Chemin de Fer du Nord in France in 1911. Since it was designed for the Paris-Saint Petersburg express, it was named the Baltic after the Baltic Sea, which was a logical extension of the naming convention that started with the 4-4-2 Atlantic and 4-6-2 Pacific.
The first 4-6-4 in the United States of America, the J-1 of the New York Central Railroad, was built in 1927 to the railroad’s design by the American Locomotive Company (Alco). There the type was named the Hudson after the Hudson River.
The world speed record for steam locomotives was held by a 4-6-4 at least twice. In 1934 the Milwaukee Road’s class F6 no. 6402 reached 103.5 miles per hour (166.6 kilometres per hour), and in 1936 the German class 05.002 reached 124.5 miles per hour (200.4 kilometres per hour). That record was broken by the British 4-6-2 Pacific no. 4468 "Mallard" on 3 July 1938, when it reached 126 miles per hour (203 kilometres per hour), still the world speed record for steam traction.
Tank locomotives 
The 4-6-4T was also a fairly common wheel arrangement for passenger tank locomotives. As such it was essentially the tank locomotive equivalent of a 4-6-0 tender locomotive, with water tanks and a coal bunker supported by four trailing wheels instead of in a tender.
The first known 4-6-4T tank locomotive was rebuilt from a Natal Government Railways (NGR) K&S Class 4-6-0T, that was modified in 1896 to enable it to run equally well in either direction on the Natal South Coast line, where no turntables were available at the time. This sole locomotive later became the Class C2 on the South African Railways (SAR). The first known locomotive class to be designed with a 4-6-4T wheel arrangement, the NGR’s "Neilson Reid" tank locomotive, was based on this modified locomotive and built by Neilson, Reid and Company in 1902. These became the Class E on the SAR.:87-89, 96-98:28-30
- Tender locomotives
Seventy R class 4-6-4 Hudson tender locomotives, the only class of this configuration in Australia and built by North British Locomotive Company, were introduced by the Victorian Railways in 1951 for mainline express passenger operations. However, the introduction in 1952 of the B class diesel-electric locomotives saw the R class almost immediately being relegated to secondary passenger and freight use, with many being staged at depots around the state. A number were preserved and some of these continued to operate on special excursion trains.
With the privatisation of regional passenger operations in Victoria in the mid-1990s, two R class locomotives were brought back into normal revenue service by the West Coast Railway, for regularly scheduled mainline passenger trains between Melbourne and Warrnambool. The locomotives underwent a number of modifications to allow for reliable high speed operation, including dual Lempor exhausts, oil firing and the addition of a diesel control stand for multiple unit operation. The use of these R class locomotives on the Warrnambool line did not continue after the demise of the private operator in 2004.
- Tank locomotives
The 4-6-4T tank locomotive configuration was a popular type with the Western Australian Government Railways. The D class was introduced for suburban passenger service in 1912. Its successors, both also of the 4-6-4T wheel arrangement, were the Dm class of 1945 that was rebuilt from older E class 4-6-2 Pacific tender locomotives, and the Dd Class of 1946.
- Tender locomotives
The second-largest user of the 4-6-4 type in North America was the Canadian Pacific Railway (CPR) with sixty-five H1a to H1e class locomotives, numbered 2800 to 2864 and built by Montreal Locomotive Works (MLW) between 1929 and 1940. They were highly successful and improved service and journey times on the CPR's transcontinental routes. The third and later batches of CPR Hudsons, H1c to H1e numbers 2820 to 2864, were dubbed Royal Hudsons and were semi-streamlined. Royal permission was given for these locomotives to bear the royal crown and arms after locomotive no. 2850 hauled King George VI across Canada in 1939.
Five CPR Hudsons survived. H1b class no. 2816 "Empress" is the sole remaining non-streamlined CPR Hudson. It was repatriated from static display at Steamtown in Scranton, Pennsylvania, to the CPR in 1998 and was restored and converted to oil-burning to haul excursions for CPR. The other remaining H1 class locomotives are all Royal Hudsons. As at 2008 three were on display in museums, no. 2839 in California, no. 2850 in Quebec and no. 2858 in Ontario, while no. 2860, the first oil-burning Royal Hudson of the class, was operational and based in British Columbia. By 2008 the CPR Hudsons were the only operational Hudsons in North America. (Also see North American production list)
- Tank locomotives
The Grand Trunk Railway (GTR) had six K2 class 4-6-4T locomotives, built in September 1914 by MLW and acquired for suburban service. Numbered 1540 to 1545 on the GTR, they were reclassified as X-10-a and renumbered 45 to 50 after being absorbed by the Canadian National Railway (CN) in 1923. Three of them are preserved, numbers GT 1541 (CN 46) and GT 1542 (CN 47) at the Steamtown National Historic Site in Scranton, Pennsylvania, and GT 1544 (CN 49) at the Canadian Railway Museum in Delson, Quebec. (Also see North American production list)
The Finnish State Railways Class Pr2, nicknamed "Henschel", was a 5 ft (1,524 mm) gauge passenger tank locomotive class, ordered from Henschel & Son by the Estonian State Railways in the spring of 1939 and completed in 1941. The outbreak of the Second World War prevented their delivery to Estonia, but a few of these engines did operate in Latvia in 1942. They became superfluous when the Germans began converting the Baltic tracks to 4 ft 8 1⁄2 in (1,435 mm) standard gauge, and the four locomotives were sold to Finland. They were classified Pr2 and numbered 1800 to 1803 upon their arrival in Finland in December 1942.
The Class Pr2 tanks were quite advanced locomotives and were based on the Henschel-built DRG Class 62 tank engine design of 1928 for the Deutsche Reichsbahn. After their initial teething problems were solved, they proved to be fast runners and an ideal addition to the motive power stable. They were originally built as oil-burners and reverted to this type of fuel between 1947 and 1954, when oil prices were low. With its 1,830 millimetres (72 inches) driving wheels, it was very fast and one of them achieved 144 kilometres per hour (89 miles per hour) during a test run. No. 1803, the last Class Pr2 in service, was withdrawn in May 1960. Only no. 1800 has been preserved.
The four-cylinder 4-6-4 compound locomotive designed by Gaston du Bousquet for the French Chemin de Fer du Nord, of which two were built at the company's workshops in 1911, was the first tender locomotive in the world with this wheel arrangement. Named the Baltic since it was intended for service on the Paris-Saint Petersburg express, its most remarkable feature was the en echelon arrangement of the two low-pressure inside cylinders in order to accommodate the very large bore. One of them was built with an arch-tube firebox. Although they were not multiplied, they were the forerunners of the highly successful 4-6-2 Nord Pacifics and Super-Pacifics. One survives in the Musée français du chemin de fer (French national railway museum) at Mulhouse in eastern France, cut up in sectioned form to display its interior during the World Exhibition in Paris in 1937. Its tender was not preserved.
France also produced some of the last Baltic locomotives. In 1938 Marc de Caso, the last Chief Mechanical Engineer of the Nord, originated the construction of eight Baltic locomotives, all delivered to the newly established Société Nationale des Chemins de fer Français (French National Railway Corporation or SNCF). Of these eight, three were 232.R class three-cylinder simplex locomotives with rotary cam poppet valve gear, while four were 232.S class four-cylinder compound locomotives, initially also with poppet valve gear that was later replaced by Walschaerts valve gear driving oscillating cams. Built for comparative purposes, it was found that the compounds outperformed the simples.
The eighth of the class, the final French Baltic type, was completed in 1949 as the 232.U.1 class. This was another four-cylinder compound with Walschaerts valve gear, but with very large and light piston valves, that proved capable of more than 4,000 indicated horsepower (3,000 kilowatts). This locomotive is also preserved at Mulhouse. (Also see Netherlands)
- Tender locomotives
Three 4-6-4 tender locomotives were built for the Deutsche Reichsbahn (DRG) by Borsig in 1935. Classified as Class 05, they were designed for high speed running. They were three-cylinder locomotives with giant 90 inches (2,299 millimetres) driving wheels and powerful clasp brakes on all wheels. 1⁄2
The first two locomotives were conventional locomotives, but the third was built as a cab forward and burned pulverised coal. All three were built streamlined, in shrouds that covered the locomotives almost to the railhead. On 11 May 1936 the 05.002 set a world speed record of 124.5 miles per hour (200.4 kilometres per hour), that was bettered by the British 4-6-2 Pacific "Mallard" two years later, on 3 July 1938.
All three survived World War II and were rebuilt as conventional non-streamlined locomotives in 1950, with new boilers. They worked in this form until 1957, when electric locomotives took over on the high-speed routes. The first locomotive, 05.001, was restored to its original streamlined configuration in 1961, for display in the Nuremberg Transport Museum.
- Tank locomotives
A number of German 4-6-4T tank locomotive classes were built, the best known being the Prussian T 18 class of 1912. Altogether 534 of them were built by the Stettiner Maschinenbau AG Vulcan and Henschel & Son between 1912 and 1927. Of these, 458 went to the Prussian state railways and subsequently the Deutsche Reichsbahn, where they became the DRG Class 78.
There were two classes of 4-6-4 tender locomotives in India, both early in the history of the wheel arrangement and also of unusually narrow gauge. The nine G class locomotives of the 2 ft 6 in (762 mm) gauge Barsi Light Railway in western India were built by Nasmyth, Wilson and Company in 1928 and 1930 and by W. G. Bagnall in 1939. The four ND class locomotives of the 2 ft (610 mm) gauge Scindia State Railway in Gwalior were built in 1928 by Kerr, Stuart and Company.
The Indonesian C27 class locomotive of the Java Staatsspoorwegen was introduced to Java by the Netherlands colonial administration. The class was designed to meet the requirement to haul trains of 400 tons at a speed of 50 kilometres per hour (31 miles per hour) on a 0.5% incline with 180 metres (590 feet) radius curves. The locomotives also had to be able to negotiate curves with a sharp radius of 120 metres (390 feet) at a speed of 80 kilometres per hour (50 miles per hour). Between 1916 and 1922 altogether thirty-nine locomotives were ordered from three manufacturers, Werkspoor, Armstrong Whitworth and Swiss Locomotive and Machine Works. The C27 class was used on railway lines around Jakarta, Bandung and Surabaya until electrification was carried out around Jakarta between 1925 and 1930. They were then relocated to secondary lines like the Merak-Tanah Abang in Banten province, the lines around Kertosono and Blitar and also between Purwokerto, Kutoarjo and Purworejo.
From 1921 fifty-eight C28 class express passenger 4-6-4T tank locomotives were built for the Java Staatsspoorwegen by three German manufacturers, Henschel & Son, Sächsische Maschinenfabrik and Maschinenfabrik Esslingen. The C28 class was one of the most popular in Indonesia, achieving speeds of up to 95 kilometres per hour (59 miles per hour). It was declared the world's fastest steam locomotive on 1,067 mm (3 ft 6 in) Cape gauge when it achieved 110 kilometres per hour (68 miles per hour). In addition, being a tank locomotive, it was able to travel at full speed in both directions. It was used on the Jakarta-Bandung, Jakarta-Surabaya and Malang-Surabaya routes. During the Dutch colonial era, the term Vlugge Vier (Fast Four) was used on the Jakarta-Bandung route, where C28 class locomotives covered the distance of 175 kilometres (109 miles) four times a day at a speed of 65 kilometres per hour (40 miles per hour) with a travel time of about 2 hours 45 minutes. These express trains only stopped for one minute at Karawang, Cikampek and Purwakarta. In addition, the C28 class locomotive was used on express trains like the Java Nacht Express (Java Night Express) and the Eendaagsche Express (One Day Express). A C28 class locomotive also hauled the train carrying President Sukarno and his entourage to Yogyakarta on 3 January 1948.
- Between 1947 and 1949 thirty-three Class C61 locomotives were rebuilt from former Class D51 2-8-2 Mikado freight locomotives. The Class C61 was the first Japanese locomotive with the 4-6-4 Hudson wheel arrangement.
- In 1948 and 1949 forty-nine Class C62 locomotives were built with new 4-6-4 frames and using the boilers of Class D52 2-8-2 Mikado locomotives. These were the largest and fastest steam passenger locomotives to run in Japan.
- Between 1953 and 1961 forty-seven Class C60 locomotives were rebuilt from surplus Class C59 4-6-2 Pacific locomotives at the Hamamatsu and Kōriyama factories.
The Class C60 and Class C61 were smaller locomotives than the Class C62, which filled the tight Japanese loading gauge. They were equipped with Boxpok driving wheels and used several American-style appliances, even though they had British-style smokebox doors.
The Dutch Railways ordered six 4-6-4T tank passenger locomotives from Beyer, Peacock and Company in 1913. A follow-up order for thirty-four locomotives was only partly delivered when, due to the downturn in traffic caused by World War I, the Dutch authorities cancelled the remainder of the order. The forty locomotives as ordered were originally to be numbered 1201 to 1240, but the twenty-six that were delivered were later renumbered 6001 to 6026.
The fourteen undelivered locomotives were sold to the British War Department for use on the Western Front, where air-braked passenger locomotives were in short supply. They were assigned Railway Operating Division (ROD) numbers 1 to 12, 14 and 15 and were used on ambulance and troop trains as well as civilian passenger trains in the British sector.
After the war they were sold to the Chemin de Fer du Nord in France, who numbered them 3.871 to 3.884. In 1938 all fourteen passed on to the SNCF, who renumbered them 232.TB.1 to 232.TB.14. Two were withdrawn in 1946, but the rest remained in service until 1950-1951. They were outlived by their Dutch sister locomotives, of which twenty were still in service in 1952. (Also see France)
South Africa 
No 4-6-4 tender locomotives saw service in South Africa, but six 4-6-4T tank locomotive classes were used, all of them on 3 ft 6 in (1,067 mm) Cape gauge.
In 1896 the Natal Government Railways (NGR) rebuilt one of its Class K&S 4-6-0T tank locomotives to a 4-6-4T configuration, as directed by NGR Locomotive Superintendent W. Milne. This was the first known use of this wheel arrangement and was done to enable the locomotive to run equally well in either direction in shuttle service on the Natal South Coast line, where no turntables were available. In 1912, when it was assimilated into the South African Railways (SAR), this locomotive was designated Class C2.:87-89:28-29
Ten tank locomotives, designed by NGR Locomotive Superintendent G.W. Reid, were built for the NGR by Neilson, Reid and Company in 1902. Known as the "Neilson Reid" locomotives while in NGR service, they were larger versions of the rebuilt Class K&S locomotive of 1896 and many of the main dimensions were identical. This was the first known locomotive to be designed with a 4-6-4T wheel arrangement. It had a plate frame, Stephenson valve gear and used saturated steam. In 1912 they became the Class E on the SAR.:96-98:30
Eight Class F tank locomotives were placed in service on the Central South African Railways (CSAR) in 1904, designed by CSAR Chief Locomotive Superintendent P.A. Hyde and built by Vulcan Foundry. It had a bar frame, Stephenson valve gear and used saturated steam, and was acquired for the suburban services between Springs and Randfontein. The double red lining on their black livery and polished copper-capped chimneys, brass domes and boiler bands earned them the nickname "Chocolate Boxes". These locomotives retained their Class F classification on the SAR.:127-129:30
In 1905 two rack tank locomotives were built for the CSAR by Vulcan Foundry, for use on the steep rack section between Waterval Onder and Waterval Boven on the line to Mozambique. Designed as two-cylinder locomotives by Hyde, the design was modified by the builders to four cylinders, with the inner cylinders driving the rack equipment, but without a compensating increase in boiler capacity. After a new track alignment with a less severe gradient eliminated the rack section in 1908, the rack equipment was removed from the locomotives and they were re-assigned to shunting duty. In 1912 they were considered obsolete by the SAR and not classified, but they remained in service until 1915.:135-137:23
Seven Class K tank locomotives that had been built for the Manila Railway Company in the Philippine Islands by the North British Locomotive Company (NBL) in 1914, were sold to the SAR in 1917 since delivering them to the Philippines during World War I became impossible. They were superheated, had Walschaerts valve gear and were the first locomotives in South Africa to be equipped with exhaust steam injectors, which were of the Davies and Metcalfe pattern. Nicknamed "Manila", they remained in service until 1938.:33:33-34
Six Class J tank locomotives, designed by SAR Chief Mechanical Engineer D.A. Hendrie and built by Nasmyth, Wilson and Company, were introduced on the SAR in 1915. They had Walschaerts valve gear and Belpaire fireboxes and used saturated steam. Acquired to cope with increasing traffic on the Natal South Coast, but unable to handle the rapidly increasing loads due to their small proportions, they soon ended up being employed as shunters in the Durban harbour, at Mossel Bay and in the Cape Midlands, until they were withdrawn from service by 1957.:33:32
Soviet Union 
Only three prototype Hudson locomotives were built in the former Soviet Union in 1937 and 1938. They were all streamlined and were the only streamlined series of Soviet steam locomotives, although a later post-war P36 series 4-8-4 Northern locomotive was semi-streamlined. All three were scrapped in the 1950s.
- In 1937 two were built by the Kolomna Locomotive Works. These were known as the 2-3-2K locomotives, designed by Lev Lebedyanskii and rated at 3,070 horsepower (2,290 kilowatts). Designated the P12 series, they were used to haul the "Red Arrow" passenger train between Moscow and Leningrad. The intention was to build up to ten 2-3-2K locomotives to haul all express passenger trains between Moscow and Leningrad, but these plans were interrupted by World War II and not resumed.
- Another one was built in Voroshilovgrad in 1938, known as the 2-3-2V experimental locomotive number 6998. This locomotive was never used on mainline service.
United Kingdom 
- Tender locomotives
The only 4-6-4 tender locomotive in the United Kingdom was the London and North Eastern Railway (LNER) no. 10000, built in 1930 as an experimental high-pressure compound locomotive with an experimental high-pressure water-tube boiler. It was the only locomotive of the Class W1 and became known as the "hush-hush locomotive" on account of the great secrecy under which it was built. Its trailing wheels were arranged uniquely. Instead of being in one four-wheel trailing truck, the first pair was a Cartazzi axle, mounted in a rigid frame but still allowed sideways deflection against a centering force, as typical of the LNER’s practice on its Pacific locomotives. The second pair was in a two-wheel trailing truck.
The experiment proved much less successful than had been hoped and in 1936 it was rebuilt along the lines of a streamlined LNER Class A4 Pacific, though it retained its Baltic wheel arrangement. After being rebuilt, the Class W1 was still easily distinguishable from an A4 at a glance, without looking for the extra trailing wheels, by the fact that it was never officially named even though the name "Pegasus" had been proposed. It therefore became known among train spotters as the "No-name Streak".
- Tank locomotives
A number of 4-6-4T tank locomotives were built for various British railway companies. The first and longest-lived were two locomotives, built by Nasmyth, Wilson in 1904 for the narrow-gauge County Donegal Railways. Both were later superheated and one lasted until 1967, albeit derelict.
The first standard-gauge examples were Robert Whitelegg’s design in 1912 for the London, Tilbury and Southend Railway (LT&SR). They were only delivered after the LT&SR had been taken over by the Midland Railway, where they were designated the 2100 class.
Between 1914 and 1922 the London, Brighton and South Coast Railway (LB&SCR) built seven L class tank locomotives, known as the "Brighton Baltics". The first examples suffered from instability problems until they were rebuilt with well-tanks. These high-speed tank locomotives hauled the famous "Brighton Belle" train until the electrification of the Brighton Main Line in 1933, after which they were converted into N15X class 4-6-0 tender locomotives. They remained in service until 1957.
The Glasgow and South Western Railway and a number of other railways also had tank locomotive classes of this wheel arrangement.
- The Lancashire and Yorkshire Railway examples were very rare in having four cylinders. Known as the "Dreadnought Tanks", they proved to be too large and too complex for the duties they performed.
- The saturated steam tank locomotives of the Belfast and County Down Railway were spectacularly unsuccessful because of poor valve settings.
- On the other hand the Furness Railway tank locomotives, also using saturated steam and with inside cylinders, were very popular with their crews.
United States of America 
The first Hudson locomotive in North America was built in 1927 for the New York Central Railroad (NYC) by American Locomotive Company (Alco), to the railroad's design. The locomotive proved to be very successful and was named the Hudson type, after the Hudson River. Thirteen of these locomotives, one J-1 type and twelve J-3a types, were streamlined for use with named passenger trains like the "Empire State Express" and the "20th Century Limited". Between the NYC and its subsidiaries, the Boston and Albany Railroad (B&A), the Cleveland, Cincinnati, Chicago and St. Louis Railway (CCC&StL or "Big Four") and the Michigan Central Railroad (MC), they acquired altogether 275 4-6-4 locomotives of several different types, the largest Hudson fleet in North America.
The Chicago, Milwaukee, St. Paul and Pacific Railroad (Milwaukee Road) could have produced the first American 4-6-4 since its design work was done earlier than that of the NYC, but financial constraints delayed the project and the Milwaukee's locomotives only emerged in 1930. The Milwaukee called them Baltic, following the European practice started in France. The initial order of fourteen Class F6 locomotives was followed by eight more Class F6a locomotives in 1931, and in 1938 the Milwaukee acquired six streamlined Class F7 Baltics, with the shrouds designed by noted industrial designer Otto Kuhler. These took over the Milwaukee's crack "Hiawatha" express trains from the Class A 4-4-2 Atlantics and were among the fastest steam locomotives of all time. The schedules of many of these trains required extended running at 100 miles per hour (160 kilometres per hour).
In addition to the Milwaukee’s streamlined Class F7, two other railroads ordered larger and faster 4-6-4 locomotives with 84 inches (2,134 millimetres) drivers in the late 1930s. These were the Atchison, Topeka and Santa Fe Railway (Santa Fe) with its 3460 Class and the Chicago and North Western (CNW) with its Class E-4. The Milwaukee and CNW locomotives were all streamlined, and only one of the Santa Fe locomotives, the 3460 "Blue Goose".
In 1937 the Chicago, Burlington and Quincy Railroad (Burlington Route) needed backup locomotives for their streamlined diesel-hauled "Zephyr" passenger trains. Their solution was to streamline their Baldwin-built no. 3002 in their main Iowa shops. The locomotive was renumbered as no. 4000 and given the name "Aeolus", after the mythical keeper of the winds. A second streamlined 4-6-4 was built for this purpose and numbered 4001.
There were also some one-off and experimental 4-6-4 locomotives. A number were rebuilt from 4-6-2 Pacific locomotives, or in some cases from other designs.
- The Baltimore and Ohio Railroad (B&O) built four as experimental locomotives between 1933 and 1936, using Colonel Emerson’s water-tube fireboxes, but eventually turned to diesel-electric traction instead.
- In 1937 the Illinois Central Railroad (IC) rebuilt a 2-8-4 Berkshire into its only Hudson, the Illinois Central No. 1, which was not a success and was not repeated.
- The Wabash Railroad rebuilt its seven Class P1 Hudsons from their unsuccessful K-4 and K5 Class 2-8-2 Mikado locomotives.
North American production list 
Twenty-one railroads in North America owned 4-6-4s. Many were similar in concept to the NYC Hudsons, with 79 to 80 inches (2,007 to 2,032 millimetres) driving wheels, but most were a little larger than the NYC locomotives, such as the F6 and F6a classes of the Milwaukee Road, the K-5-a class of the Canadian National, the Canadian Pacific locomotives, the S-4 class of the Burlington Route, the I-5 class of the New Haven and the 1151 class of the Lackawanna. There were also the lightweights, which include the L-1 class of the Nickel Plate Road, the class D of the Maine Central and the class NR-1 of the Ferrocarriles Nacionales de México (N de M). On these the extra axle was used to reduce the axle load in comparison to a 4-6-2 Pacific locomotive.
Because the 4-6-4 design was really only optimally suited to express passenger trains which were dieselised early, the Hudsons were early candidates for withdrawal and scrapping. None of the NYC locomotives survives and neither does any of the Milwaukee locomotives. Five Canadian Pacific Hudsons survive, including four Royal Hudsons and the non-streamlined Canadian Pacific 2816. Five of the Burlington Route locomotives survive, including the "Aeolus". Other surviving Hudson locomotives are two each of the Santa Fe and Canadian National, and single examples from the Chesapeake and Ohio Railway, N de M and Nickel Plate Road.
|Railroad||Qty||Class||Road numbers||Builder||Build years||Notes|
|GT||6||K2||1540–1545||Montreal||1914||Tank engines. Later CN 45–50, class X-10-a|
|MC (NYC)||10||J-1b||8200–8209||ALCO||1927||Renumbered NYC 5345–5354|
|5||J-1c||8210–8214||ALCO||1929||Renumbered NYC 5355–5359|
|15||J-1d||8215–8229||ALCO||1930||Renumbered NYC 5360–5374|
|6||3460||3460–3465||Baldwin||1937||One streamlined (No. 3460)|
|B&A (NYC)||5||J-2a||600–604||ALCO||1928||Renumbered NYC 5455–5459|
|5||J-2b||605–609||ALCO||1930||Renumbered NYC 5460–5464|
|10||J-2c||610–619||Lima||1931||Renumbered NYC 5465–5474|
|CCC&StL (NYC)||20||J-1d||6600–6619||ALCO||1929||Renumbered NYC 5375–5394|
|10||J-1e||6620–6629||ALCO||1931||Renumbered NYC 5395–5404|
|5||H1e||2860–2864||Montreal||1940||Streamlined, oil burner|
|8||F6-a||6414–6421||Baldwin||1931||Renumbered 142–146, 139–141|
|CBQ||12||S-4||3000–3011||Baldwin||1930||3002 rebuilt as class S-4A 4000 Æolus|
|1||S-4A||4001||CB&Q Burlington||1938||New, streamlined, named Æolus|
|B&O||1||V-1||5047||B&O Mt Clare||1933||Rebuilt from P-1 class|
|1||V-2||2||B&O Mt Clare||1935||New; renumbered 5340|
|1||V-3||5350||B&O Mt Clare||1935||New|
|1||V-4||5360||B&O Mt Clare||1936||New|
|IC||1||–||1||IC||1937||Rebuilt from 2-8-4 No. 7038|
|N de M||10||NR-1||2700–2709||ALCO||1937|
|SLSF||10||1060||1060–1069||SLSF||1937–1941||Rebuilt from 4-6-2s|
|5||L-1||490–494||C&O||1946–1947||Rebuilt from 4-6-2; four streamlined|
|WAB||7||P-1||700–706||WAB Decatur||1943–1947||Rebuilt from 2-8-2s|
- Railway Technical Web Pages (Steam Locomotive Glossary)
- Reed, Brian. (1972). Loco Profile, Nord Pacifics. Windsor: Profile Publications.
- 4-6-4 "Hudson" Type Locomotives
- DB Museum in Nuremberg - Germany’s fastest steam locomotive
- Holland, D.F. (1971). Steam Locomotives of the South African Railways, Volume 1: 1859-1910 (1st ed.). Newton Abbott, Devon: David & Charles. ISBN 0715353829.
- Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. ISBN 0869772112.
- Oberg, Leon (2007). Locomotives of Australia 1854-2004. Rosenberg Publishing. pp. 247–248. ISBN 1-877058-54-8.
- West Coast Railway Modernised R Class Locomotives R711 & R766
- Anatomy of West Coast Railway's "Super" R Class, Introduced and compiled by Barry Merton
- CP2816 - Rebirth of a mechanical Wonder. (CPR News, Number 2, 2001)
- Pölhö, Eljas; Pykälä-Aho, Mia (1996). Suomen juna- ja raitiovaunukuvasto (Finnish Motive Power). ISBN 91-7266-133-X
- Sakari K. Salo (2009): Höyryveturikirja, s. 14. Helsinki: Kustantaja Laaksonen. ISBN 978-952-5805-12-3
- The Railfaneurope.net Picture Gallery
- Ransome Wallis (ed). Concise Encyclopedia of World Railway Locomotives
- Chapelon, Andre. La Locomotive a Vapeur
- Ebel, Jürgen-Ulrich; Knipping, Andreas; Wenzel, Hansjürgen (1990). Die Baureihe 78: Bewährt in sechs Jahrzehnten: Preußens - T 18. EK-Verlag, Freiburg. ISBN 978-3-88255-547-9
- Dietmar Falk: Die schnelle Preußin. Erinnerung an die T 18. In: LOK MAGAZIN, Nr. 265/Jahrgang 42/2003. GeraNova Zeitschriftenverlag GmbH München, S. 50-60. ISSN 0458-1822
- Henschel-Lieferliste (Henschel & Son works list), compiled by Dietmar Stresow
- Inoue, Kōichi (1999). 国鉄機関車辞典 [JNR Locomotive Encyclopedia]. Japan: Sankaido. pp. 48–49. ISBN 4-381-10338-6.
- Aves, William A. T. (2009). The Railway Operating Division on the Western Front. Donnington, Lincolnshire, UK: Shaun Tyas Publishing. p. 173. ISBN 1-900289-99-7.
- Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. ISBN 0715354272.
- Cox, Stewart, Locomotive Panorama Vol 1
- Patterson, Edward M, The County Donegal Railways
- Bradley, D.L., Locomotives of the London, Brighton and South Coast Railway (RCTS) Vol 3
- Fryer, C.E.J.,British Baltic Tanks
- Burlington Builds Streamline Steam Locomotive. Railway Age. 1937. Retrieved 6 March 2012.
- Sagle, Laurence, B&O Power