4-6-4
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.
The first 4-6-4
tender locomotive 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 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,
Baltimore & Ohio,
Boston & Albany,
Big Four,
Canadian National,
Chesapeake & Ohio,
Burlington,
Chicago & North Western,
Lackawanna,
Illinois Central,
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.
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.
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.
A number of 4-6-4
tank locomotives were built for various
British railway companies. The
London, Brighton and South Coast Railway built seven Remembrance Class tank locomotives between
1914 and
1922; these high-speed tank locomotives hauled the famous
Southern Belle until
electrification 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 and the Glasgow and South Western Railway 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 practise, being mounted in a rigid frame but allowed sideways deflection against a centering force. The second pair were in a two-wheel trailing truck. Thus some claim No. 10000 was not a true 4-6-4 but more of a 4-6-2-2. 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".
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.
|
West Coast Railways' R711 locomotive in modified form |
Seventy R class 4-6-4 tender locomotives were introduced by the
Victorian Railways in 1951 for mainline express passenger operations. 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. 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.
*
4-6-4 or Hudson*
German Wikipedia on 4-6-4 class 05*
Anatomy of West Coast Railway's "Super" R Class*
:Category:4-6-4 locomotives
