4-6-0 Steam Locomotives in Great Britain

Class H15 (Locobase 5200)

Robert Urie's express-passenger six-coupled with outside cylinders, the first of several classes built to the same basic design. OS Nock (RWC IV, pl 178) notes the extreme simplicity of the design and says they were "magnificently built in what could be termed the 'Scottish tradition.'" Glover (1967) notes that the deep firebox (9 feet long) meant that the drivers were unevenly spaced and the smokebox was elongated. (The effect must have been accentuated by coning the boiler and thus reducing the smokebox diameter.)

The first batch came in 1914 with a later addition from Eastleigh built after the London & South Western was absorbed in 1923 by the Southern Railway.

Class King Arthur (Locobase 1059)

Data from "Southern Railway "King Arthur" Class Leading Dimensions diagram; and graham Glover, British Locomotive Design 1825-1960 (London: George Allen & Unwin Ltd, 1967), p.36. See also Southern Railways E-mail List Group [] (first visited October 2002, last accessed as [], 13 August 2025.) North British Locomotive Company works numbers were 23209-23214 in May 2025, 23215-23223 in June; 23224-23226, 23228 in July; 23227, 23229 in August, , 23279-23288 (road 763-792) in 1925.

Virtually identical specifications to the Great Western's Castles, except that the King Arthurs featured two cylinders rather than four. Otherwise, a similar small boiler (63" in diameter) and grate being worked hard.

Glover noted that this design was an evolution of Ten-wheelers operated by the Southern's pre-grouping ancestor London & South Western. Named for knights of the Round Table, they were built in several batches.

SEMG's account explains in more detail. Richard Maunsell, first CME of the Southern Railway evaluated the N15 design and revised the front end. The changes, which included "increasing the area of the steam and exhaust ports, fitting a modified chimney and blast pipe significantly improved the class' performance." [] (29 October 2004) added other changes that included long-lap valves and a rise in boiler pressure. Moreover, improved driver balancing reduced the N15's hammer-blow on the track, softening the ride and contributing to longer track life.

Maunsell's rejuvenation of Urie's N15s proved to be a big success, so much so that when the Lord Nelson design was delayed, the Southern ordered 20 more N15s from North British Locomotive Company. Maunsell did tinker with the proportions, however, raising the boiler pressure, shrinking the cylinder diameter, and modifying the cab profile to fit the Southern's loading gauge.

In addition to the North British engines built in Glasgow and thus known as "Scotchmen" to their crews, Southern's Eastleigh works itself added 10 to replace retiring G14s. Later orders added 10 to the North British order and another 14 to the Eastleigh output. During this period, Southern's decision to name its locomotives resulted in the Round Table affiliation.

SEMG's valedictory rings firmly positive:

"After a poor start, this class emerged as one of the greatest designs of its day. They were popular with their crews and had a reputation for both being reliable and having an impressive preformance."

The Maunsell Society's newsletter published Clive Groome's delightful memoir, presented on the [] page (first visited November 2002, link no longer available). Groome's generalization about all of the Urie/Maunsell H, N (King Arthur), & S15 designs:"[They] did nothing on less than full open regulator and almost everything on 25% cut off. They could all be fired on dust over the half door flap for mile after mile."

But the Lord Nelsons were more powerful and Bulleid's Merchant Navy and West Country Pacifics soon pushed the King Arthurs into the background. The first was retired in 1953 and all were out of service by 1962.

Class Lord Nelson (Locobase 2513)

Described by Hollingsworth (1982). See also "Maunsell "Lord Nelson" class 4-6-0" on the Southern E-Group's website at [], last accessed 31 March 2017; Mark Fry, "Vol 17: The Hero's Return 850 Lord Nelson"

posted on September 28, 2012 on the Steam Age website at [], last accessed 31 March 2017; "Southern Railway - Four-cylinder Express-Locomotive", Engineer (19 November 1926),, pp. 559-560.

Hollingsworth describes the class as "noble engines", these engines were also "a magnificent but rather complex four-cylinder 4-6-0." In fact, the design was right in line with British express engine practice, showing a Belpaire boiler and smallish grate and modest superheater area. Their design requirement was to pull 500 ton trains at a 55 mph (89 kph) start-to-stop average between London's Victoria Station and Dover.

Remarkably, fitting two sets of Walschaerts gear inside along with the two sets outside didn't cause many problems. (See the Engineer account for a thorough detailing of counterbalance considerations adopted "in accordance with Professor W E Dalby's method.") One result of the four cranks being set at 135 deg, according to the Eastleigh Railway Preservation Society's website, is "eight softer 'puffs' per revolution of the driving wheels rather than four heavy ones and therefore produce a more even 'pull' on the fire." (See Locobase 2362 for a similar, and earlier, crank arrangement in a single four-cylinder 0-6-0T designed by the North Staffordshire's J A Hookham.

Because of a flat section in the rear of the firebox, however, a Lord Nelson needed "very skillful firing if it was to steam properly." In addition, notes the ERPS, the coal had to be hand-thrown as much as 10 feet from the fire hole. The Steam Age blog quotes S. C. Townroe (from his (Arthurs, Nelsons and Schools At Workö (Ian Allen, 2nd edition, 1983)) on the unhappy outcome of a failure to meet the challenge: (If the fireman was unable to shoot shovelfuls of coal to the far front of the box, two things happened: the unfed areas of the grate would burn thin and large volumes of cold air would be drawn in, and coal which fell short of its intended place would form a high ridge across the middle of the grate, to add further to the difficulty of hitting the front.ö

On the other hand, all sources note that the maintenance staff liked these engines for their reliability, as they averaged 200,000 miles (322,000 km) between failures.

Fitting Lemaitre multiple-jet blast pipes in the late 1930s, a decision taken by OVS Bulleid, improved air flow over the fire and relieved the firemen to a great extent. Bulleid also replaced the 8" (203 mm) piston valves with 10" (254 mm) diameter valves, although at least one engine never received this upgrade. Still, these engines always required a careful touch to run well, even, Hollingsworth notes, in excursion operation after their retirement.

Class S15 (Locobase 2296)

As explained on the Maunsell Society's website ([]) these were Maunsell's adoption of the Robert Urie S15 design (see Locobase 2297) that had served freight trains well for several years. One change in the design was the widening of the firebox's water legs to improve circulation, which reduced the grate area by 2 square feet.

The first batch of 15 was delivered in 1927 and 10 more followed in 1936. The subject of theMaunsell site's description, 830, cost 6,585 pounds when new, operated for 35 years, and racked up 1.2 million miles.

Heating surface data from OS Nock (Southern Steam, 1968).

The Maunsell Society's newsletter published Clive Groome's delightful memoir of working the S15s and presented on the [] page (visited November 2002). Groome describes thse "classic South Western 'chonkers'" as "lovely machines." Admittedly, there were challenges posed in operating them. For one thing, the cab designed induced a vaccuum at speed that caused dust, hot water, and dirt to swirl around in the cab.

More confounding to the neophyte, "these long stroke, heavily built two cylinder locomotives were prone to throw themselves back and forth into the tender as they gained velocity." The result was that the coal was shuffled forward right out of the tender and onto the footplate. Sometimes, Groome notes, this bed piled up to a depth of 3-4 inches that pinned the cab door shut. At those times the crew had to dig themselves out!

Besides this and the swirling water and dust, "the ears and bodies of the heroic crews were pounded as the reverser kicked noisily against the latch and the axleboxes thuded like the hammers of Thor through the floorboards." Vibration caused the brakes to "automatically" apply, dampers to shake themselves shut, and the injector to stick open or closed.

But Groome found these locomotives could run hard and long with 25% cutoff all the while and no priming. (see also the comments under the L&SW H15 entry).

They endured well into the 1960s.

Class T14 - superheated (Locobase 3132)

Data from "Rebuilt Four-Cylinder Six Coupled Engine, London & South Western Railway", The Locomotive, Vol XXII, No 281 (15 January 1916), p. 1. See also [], last accessed 26 June 2014.

When Drummond's T14s (Locobase 2306) were superheated, they were run at a lower boiler pressure, which doubtless extended their lifetimes. (The boiler demand factor was almost identical, indicating an intention to achieve performance improvements through superheating alone.) In addition, although they had the same tall drivers, they ran in secondary service.

H Holcroft commented on several topics covered by C S Cocks's History of Southern Railway Locomotives to 1938. These comments were summarized in [] (visited 30 Jan 2005). As quoted by SI, Holcroft wondered at the T14's "charmed life" given their shortcomings: "They had shallow fireboxes, and therefore could not be worked hard, the valve gear was poor, the bearing surfaces were inadequate, and they were condemned to drag about enormous tenders holding nearly 6,000 gallons of water." The compiler adds Holcroft's opinion that "the running people must hide these relics away in the darkest recesses of their gloomy sheds as a reserve, bringing them out at peak holiday periods when anything that would turn a wheel was welcome."

Whew! Far from the sentimental rosiness of most evaluations. R W Urie took the four in the class that still had saturated boiler--443, 445-446,. 458-- in hand a few years later to try to remedy the design's deficiencies. The contemporary account cited above clearly describes the installation of a home-built smokebox superheater and the removal of the water tubes.

Eventually Urie refitted all ten with the installation. In 1930-1931, Maunsell installed fire-tube superheater. At the same time he deleted the large splashers over the drivers and fitted mechanical lubricators. But, says the Southern E-Group's entry on the T14, " there was still no sign of any marked improvement in performance."

It took what the E-Group describes as a "logistical accident" to make a difference: "N447 required a replacement chimney in October 1940 but no spares were available and so a short stove-pipe chimney, all that was available at the time, was somehow fitted. Remarkably, there was a marked improvement in its steaming abilitity. The same enhancement was subsequently applied to all but one of the class as they went through Eastleigh works."

Wikipedia's assessment is a little more generous: "[T]heir potential in secondary duties gave Maunsell the opportunity to attempt to right the problems associated with the original design. Superheating helped to solve the problems of efficiency in terms of coal and water, whilst the removal of the splashers meant ease of access to the wheels and airflow to the axleboxes." The article also notes that fitting a short "stove-pipe chimney" to 447 in 1940 in place of the Drummond design (because of lack of spares) produced the unexpected result of "...a marked improvement in its steaming abilitity due to the improved draughting that resulted in the freer blast. The same enhancement was subsequently applied to all but one of the class as they went through Eastleigh works for overhaul."

Note: Wikipedia relied on Haresnape, B. & Rowledge, P.: Drummond Locomotives: A Pictorial History (Hinckley: Ian Allan Publishing,1982) ISBN 0711012067, for the comments reproduced above.

458 was irreparably damaged during a 1940 bombing raid. The others survived up to a decade longer before being retired in 1948-1951.