A subsequent development was as an elongated 2-8-4 Berkshire type that required extra driving wheels to remain within axle load limits.

One locomotive, numbered 801, was built for the CF du Bas-Congo au Katanga by Société Anonyme John Cockerill in 1939.

The locomotive is believed to have been built for the line between Bukama and Kamina and accumulated 1,200,000 km (750,000 mi) during its service lifetime.

Their Canadian type name was after the Selkirk Mountains across which they were placed in service, the railway summit of which was located just inside the western portal of the Connaught Tunnel beneath Rogers Pass.

Modifications to the original design led to the T1b being 10 tonnes lighter while its operating steam pressure was increased from 275 to 285 psi (1,900 to 1,970 kPa).

In 1937, the South African Railways (SAR) placed one 3 ft 6 in (1,067 mm) Cape gauge 2-10-4 Class 21 steam locomotive in service, designed for mixed traffic and suitable for light rail.

It was designed by A.G. Watson, chief mechanical engineer of the SAR from 1929 to 1936, and built by the North British Locomotive Company in Glasgow.

It was the only example built, and represented the maximum power obtainable on Cape gauge from a non-articulated locomotive limited to a 15 long tons (15.2 t) axle load and 60 lb/yd (30 kg/m) rail.

The first of the 1944 batch produced 5,600 drawbar horsepower (4.2 MW) on road test, the highest figure known for a two-cylinder steam locomotive.

A version of the Berkshire with 10 driving wheels instead of eight was an obvious development and the first to be delivered were to the Texas and Pacific Railway, after which the type was subsequently named.

The four-wheel trailing truck allowed a much larger firebox, thus a greater ability to generate heat, and thus steam.

The Superpower design, as Lima's marketing department called it, resulted in a locomotive that could develop great power at speed while not running out of steam-generating ability.

Calculated tractive force was 102,106 lbf (454.19 kN), average weight was over 500,000 lb (230 t), and boiler pressure was 250 psi (1.7 MPa).

The Chicago Great Western Railway was an unusual customer for 2-10-4s as it was a 'granger' railroad, operating in the predominantly flat Midwestern United States.

All had 63" diameter drivers, 29" x 32" cylinders and a 255 psi boiler pressure - the same basic specification as the successful Texas & Pacific fleet of 2-10-4s.

The 2-10-4s allowed the CGW to dramatically improve its operational efficiency - trains could be heavier yet faster and double heading and banking was eliminated in many locations.

Fewer trains hauling more tonnage allowed the railroad to cut many jobs, so the new big locomotives were not well-received by employees.

The 2-10-4s promoted a new way of working on the CGW, which adopted a principle of fewer but much longer and heavier trains - a practice usually seen on transcontinental railroads in the West rather than granger routes in the prairies.

It still betrayed its foreign heritage by lacking the PRR trademark Belpaire firebox and by having a booster engine on the trailing truck.