4-6-4

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One of the streamlined NYC Hudsons that hauled the 20th Century Limited.

A 4-6-4 locomotive, in the Whyte notation for the classification of steam locomotives, has four leading wheels (generally arranged in a leading truck), six coupled driving wheels and four trailing wheels (often but not always in a trailing truck). The equivalent UIC classification is 2'C2'. The type is sometimes called the Hudson or Baltic.

The 4-6-4 is best seen as combining the basic nature of the 4-6-2 'Pacific' type with an improved boiler and larger firebox that required extra support at the rear of the locomotive. Generally the available tractive effort was little different from that of the Pacific, but steam-raising ability was increased, giving more power at speed. 4-6-4s were best suited to high-speed running across flat country. The type has fewer driving wheels than carrying wheels and thus a smaller percentage of the locomotive's weight is available for traction compared to other types. For starting heavy trains and slogging on gradients, a 4-6-4 really needs a booster engine, but for sustained long grades, more pairs of driving wheels are better.

The world speed record for steam locomotives was at least twice held by a 4-6-4; the Milwaukee Road's class F6 #6402 in 1934 with 103.5 mph, and German 05 002 in 1936 with 124.5 mph (200.4 km/h).

4-6-4 was also a fairly common wheel arrangement for a passenger tank locomotive—basically, a double-ended Pacific, able to travel in both directions with equal facility.

1 North America
2 Japan
3 France
4 United Kingdom
5 Germany
6 Australia
7 New Zealand
8 See also
9 References
10 External links

[edit] North America

The first 4-6-4 tender locomotive in North America was built in 1927 by ALCO for the New York Central Railroad, and to the NYC's design. The locomotive proved very successful and was named the Hudson type after the Hudson River. The NYC acquired 275 Hudsons, the largest fleet in North America, of several different types.

The Milwaukee Road could have produced the first American 4-6-4; its design was earlier than the NYC's, but financial constraints delayed the project, and Milwaukee's locomotives emerged later. The Milwaukee called them Baltics, and that name was fairly widely used also. The initial order of 14 class F6 locomotives was joined by 8 more of class F6a a year later in 1931, and in 1938 the road acquired 6 streamlined F-7 Baltics with shrouds designed by noted industrial designer Otto Kuhler. These took over the Milwaukee's crack Hiawatha expresses from the class A 4-4-2 Atlantics, and were among the fastest steam locomotives of all time. Schedules of many of these trains required extended running substantially above 100 mph.

The second-largest buyer of the type in North America was the Canadian Pacific Railway, which bought 65. They were highly successful in improving service and journey times on the CPR's transcontinental routes. The newer CPR Hudsons were called 'Royal Hudsons' and were semi-streamlined. Royal permission was given for these locomotives to bear the royal crown and arms after such a locomotive hauled King George VI across Canada in 1939.

Twenty railroads in North America owned 4-6-4s; these included, as well as the foregoing, the Santa Fe, Boston & Albany, Big Four, Canadian National, Chesapeake & Ohio, Burlington, Chicago & North Western, Lackawanna, Illinois Central (the only example of a Hudson designed for freight haulage), Maine Central, Michigan Central Railroad, National Railway of Mexico, New Haven, Nickel Plate, Frisco, and Wabash.

Many 4-6-4s were similar in concept to the NYC's Hudsons, with 79-80 inch driving wheels, but most of these were a little larger than the NYC's locomotives. Included in this group are the Milwaukee's F6 and F6a, the Canadian National and Canadian Pacific locomotives, the Burlington's, the New Haven's, and the Lackawanna's.

A group of railroads ordered larger, faster 4-6-4s with 84 inch drivers; these included the Milwaukee's F7, the Santa Fe's 3460 class locomotives, and the Chicago and Northwestern's. The Milwaukee and CNW locomotives were all streamlined, while one of the Santa Fe's was.

The other main grouping of North American 4-6-4s are the lightweights, which include the Nickel Plate's locomotives, the Maine Central's, and the Nacionales de Mexico examples. In these, the extra wheels were used to reduce the axle load in comparison to a 4-6-2 "Pacific".

Finally, there were many one-off and experimental 4-6-4s. A number were rebuilds from Pacifics, or in some cases other designs. Baltimore & Ohio built four examples as experimentals, using Colonel Emerson's water-tube fireboxes, but eventually turned to diesels instead. ^[1]

Because the 4-6-4 design was really only good for express passenger trains, which dieselized early, Hudsons were early candidates for withdrawal and scrapping. None of the NYC's locomotives survive; neither do the Milwaukee's. Five Canadian Pacific Royal Hudsons survive, as do four of the Burlington's, two each of the Santa Fe's and Canadian National's, and single examples from the C&O, NdeM and Nickel Plate.

[edit] Japan

The Japanese National Railways built three classes of rather advanced, American style 3'6" (1,067 mm) gauge Hudsons, classes C60 (47 built), C61 (33 built) and C62 (49 built). The C60 and C61 were smaller and the C62 was a larger locomotive, filling the small Japanese loading gauge. All were officially rebuilt from earlier locomotives of different arrangement, but it is believed that this was for accounting purposes rather than any real cost saving; the parts re-used appear to have been minimal. They were all equipped with disk drivers and much in the way of American-style appliances, although they had British-style smokebox doors.

[edit] France

The first 4-6-4 tender locomotives in the world were the two four-cylinder compounds designed by Gaston du Bousquet for the Chemin du Fer du Nord and built at the company's workshops in 1911.

They were allegedly designed to pull the Paris - St Petersburg express, and hence the title Baltic. But the name was obviously a logical extension of the convention started with 'Atlantic' and 'Pacific'.

Their most remarkable feature was perhaps the arrangement of the two low-pressure inside cylinders en echelon so as to accommodate the very large bore. One had a water-tube firebox. They were not multiplied, but gave place to the highly successful Nord Pacifics and Super-Pacifics which followed.

One survives, in sectioned form in the Cité du Train at Mulhoues in France. See http://www.railfaneurope.net/pix/fr/steam/misc_Nord/pix.html

France also produced some of the last Baltics. In 1938 Marc de Caso, the last CME of the Nord, originated the construction of eight Baltics, all delivered to the newly-created SNCF, the nationalised French railway system. Of these eight, four were built as four-cylinder compounds, with rotary cam poppet valve gear, later replaced by Walschaerts gear driving oscillating cams; three were built as three cylinder simples, also with rotary cam popppet valve gear. The compounds clearly outperformed the simples.

The eighth, and final, French Baltic completed in 1949 as 232 UI, and is also preserved in Mulhouse. This was another four-cylinder compound with Walschaerts valve gear, but in this final form driving very large and light piston valves. It proved capable of more than 4000 i.h.p.

[edit] United Kingdom

A number of 4-6-4 tank locomotives were built for various British railway companies. The first were Robert Harben Whitelegg's design for the London, Tilbury and Southend Railway in 1912. 'The London, Brighton and South Coast Railway built seven L (Remembrance) Class tank locomotives between 1914 and 1922. The first examples suffered from instability problems until rebuilt with well-tanks. These high-speed tank locomotives hauled the famous Southern Belle until electrification of the Brighton Main Line in 1933, after which they were converted into N15X class 4-6-0 tender locomotives, remaining in service until 1957. The Lancashire and Yorkshire Railway, Furness Railway, Belfast and County Down Railway and the Glasgow and South Western Railway (Whitelegg's second attempt) also had classes of this wheel arrangement.

The only 4-6-4 tender locomotive in Great Britain was LNER No. 10000, built in 1930 as an experimental high-pressure compound locomotive with an experimental water-tube boiler, and known as the "hush-hush" locomotive on account of the great secrecy with which it was built. The experiment proved much less successful than hoped, and in 1936 it was rebuilt along the lines of a streamlined LNER Class A4 Pacific, though it retained its unique wheel arrangement. It was the only locomotive of Class W1. Its trailing wheels were arranged uniquely; instead of being in one 4-wheel trailing truck, the first pair were instead a Cartazzi axle, as typical of LNER Pacific practice, being mounted in a rigid frame but allowed sideways deflection against a centering force. The second pair were in a two-wheel trailing truck. After its rebuild, the W1 was easily distinguishable from an A4 at a glance, without looking for the extra trailing wheels, by the fact that it was never named; it was therefore known to train spotters as "the no-name streak".

However the London Midland and Scottish Railway seriously considered a 4-6-4 development of its Coronation Pacific for Anglo-Scottish services in the years just before the Second World War.

This would have had 300 psi boiler pressure, four cylinders, mechanical stoking and many features in common with a 4-8-4 fast freight engine. But the advent of the war prevented this entirely practical proposition from ever seeing the light of day.

[edit] Germany

05 001 as preserved in the DB Museum, Nuremberg

In addition to a number of 4-6-4 tank locomotives (the best known being the K.P.E.V. T18, later numbered as class 78), three 4-6-4 tender locomotives were built in 1935. Classified as Class 05, they were designed for high speed running; they were 3-cylinder locomotives, with giant 90½ inch driving wheels and powerful clasp brakes on all wheels. The first two locomotives, 05 001 and 05 002 were conventional locomotives, but the third, 05 003 was built as a cab forward, burning pulverised coal. All were built streamlined, in shrouds that covered the locomotives almost to the railhead. In 1936, 05 002 set a world speed record of 124.5 mph (200.4 km/h) which soon afterwards was beaten by the LNER's famous Mallard.

All three survived World War II and were rebuilt as conventional, unstreamlined locomotives in 1950 with new boilers, in which form they worked until 1957 when electric locomotives took over the high-speed routes. The first locomotive, 05 001, was restored to its original streamlined configuration and placed into a museum in 1961.

[edit] Australia

West Coast Railway's R711 locomotive in modified form

Seventy R class "Hudson" 4-6-4 tender locomotives were introduced by the Victorian Railways in 1951 for mainline express passenger operations. These engines developed 32,080 lbs of traction, which was was less than the single H Class 4-8-4 locomotive and also less than the three ageing S Class 4-6-2 locomotives operating on the Victorian railways.^[2] The R Class were fitted with mechanical stokers and one R707 had a 'Stug' device fitted enabling the locomotive to be fired with pulverised brown coal.^[3] However, the introduction in 1952 of B class diesel electric locomotives saw the R class almost immediately relegated to secondary passenger and freight use, with many put into storage at depots around the state. During the wheat harvest season it was a common sight to see the R class at work hauling grain trains. A number were preserved and some of these continue 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 into service for regularly scheduled mainline passenger trains between Melbourne and Warrnambool. The locomotives featured 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. Sadly for steam enthusiasts, the use of these R class locomotives on the Warrnambool line did not continue after the demise of the private operator in 2004.

[edit] New Zealand

The New Zealand Railways Department did not use the 4-6-4 arrangement for any tender locomotives, but it was the wheel arrangement for a number of tank locomotive classes. The first such examples were built in 1902, when three B class tender locomotives entered the Addington and Hillside workshops and emerged rebuilt as tank locomotives and classified as the W^E class. In 1910, the Railways Department's Chief Mechanical Engineer A. L. Beattie designed a number of original 4-6-4T locomotives, the W^G class, and two further classes with the 4-6-4T arrangement followed in later years, the W^AB/W^S class and the W^W class.

[edit] See also

Category:4-6-4 locomotives

[edit] References

^ Sagle, Laurence, B&O Power
^ Victorian Railways (1954). Power Parade: Centenary Edition 1854-1954. Victorian Railways Public Relations and Betterment Board, pp. 32 & 34-35.
^ Power Parade, p. 35