In 1900, Burma Railways received five meter-gauge Fairlie locomotives from Vulcan Foundry. They had two bogies, each consisting of three coupled axles with same-size cylinders. Their difference compared to earlier Double Fairlies was that they had two separate boilers which were not joined by a common firebox. This layout was sometimes called “modified Fairlie” in this time, but had nothing in common with the Modified Fairlies built for the South African Railways more than 20 years later.

Their fireboxes were of the Belpaire type and had Drummond cross water tubes which further increased their heating surface. Each firebox was fed by one fireman, so that three people worked in the cab. Most of the time, the locomotives took a separate water tender with them.

After the “Livingston Thompson” was the last original Ffestiniog Double Fairlie to be retired due to wear and tear in 1971, continuing to run the railway with this type of locomotive was an option. Since rebuilding the locomotive would have required too much effort, the decision was made to completely build a new locomotive. This was one of the first times in history that a heritage railway had a steam locomotive built from scratch. Today there are several examples that follow the same pattern.

Since the locomotive, christened the “Earl of Merioneth”, had to complete everyday service on the tourist line, it was built with a few differences compared to its historical predecessors. The biggest difference was the significantly larger supplies, which should allow use without many intermediate stops. Oil was used as fuel to reduce the risk of forest fires due to sparks. Despite using refurbished bogies from older locomotives, it was able to haul trains with twelve cars and 500 passengers on a gradient of 1 in 80.

After many years in service, it was converted to coal-firing to reduce costs in view of the increased oil price. The chimneys had to be fitted with spark arrestors to further reduce the risk of fire. When the boiler deadline threatened to expire in 2018, the decision was the same as in the 1970s. This time, too, the decision was made to let the deadline expire and to build a new locomotive with the name “James Spooner”. Today the “Earl of Merioneth” is on display in Boston Lodge.

Class II K consisted of two Fairlie locomotives built by the British firm R. & W. Hawthorn for the Saxon narrow gauge railways. Their design made them unique among the German railways, but their blatant defects prevented the procurement of series machines. These locomotives were procured because the right design was sought for the routes with many bends and gradients. Fairlie locos basically consisted of two backwards-connected engines and thus had two boilers with two complete engines that worked independently and had to be operated simultaneously by the fireman.

This type of construction was particularly suitable for the narrow radii, since the running gear was mounted on bogies and thus allowed a great deal of freedom of movement. However, the operation presented a very big challenge, at least for the second man, since he had to load and control both fireboxes at the same time. Added to this was the tight space in the driver's cab, which hardly allowed freedom of movement.

Mainly for the latter reason, no further II K were procured and instead the III K was developed. It was also stated that the weight was too high for the existing lines. Both prototypes remained in service until the first engine was retired in 1903 and the second in 1909. Four years later, a new double locomotive was built from two times two pieces of the I K, which were also given the designation II K. Before being named II K or K II, the locomotives were called Htn F TK, from which the characteristics of these locomotives could be derived. Htn stood for the manufacturer Hawthorn, F for Fairlie, T for tank locomotive and K finally designated all locomotives for 750 mm gauge. 

After the single 2-6-2+2-6-2 Modified Fairlie of class FC of the South African Railways, Colonel F.R. Collins specified a somewhat heavier variant that was again to be built by North British. The four locomotives were delivered in 1925 and were called class FD. They had direct competition from the class GD Garratt that had the same wheel arrangement.

In service it was found that the long rigid frame produced some problems. These included huge side overhangs when running through curves and oscillations of the water and coal tanks at speed. Also the pivot bearings had to support considerably higher weights due to the supplies being on the main frame. So ultimately the GD Garratts were more successful with 14 built. All FD locomotives were scrapped in 1949.

The “Seraing” was one of the four locomotives that took part in the Semmering competition. Its name came from the Belgian city where its manufacturer was based. It had two complete boilers which met in the middle at the firebox. Two power plants were each in a bogie. The locomotive thus anticipated the design of the Double Fairlie and is said to have basically met the requirements.

The biggest problem, however, was that the manufacturing methods for the flexible steam pipes at that time were not yet mature enough to remain permanently leak-proof. The amount of dry steam that could be extracted from the boiler was also said not to have been sufficient. It eventually finished third in the competition and was not used for long.