Used underground, the locomotives condensed their steam, and coke or smokeless coal was burnt to reduce the smoke.

However, the GWR withdrew their services in August 1863, and the Met bought their own locomotives, which needed to condense as the line from Paddingdon to Farringdon was underground.

A tender was received from Beyer, Peacock and Company of Manchester for building eighteen locomotives at £2,600 each that would be available in six months.

The design of the locomotives is frequently attributed to the Metropolitan Engineer John Fowler, but the design was a development of a locomotive Beyers had built for the Spanish Tudela-Bilbao railway, Fowler only specifying the driving wheel diameter, axle weight and the ability to navigate sharp curves.

The boiler pressure was 120 psi (830 kPa), the front wheels were on a Bissel truck and fitted with 40 cubic feet (1.1 m3) bunker.

As they were intended for an underground railway, the locomotives did not have cabs, just a simple spectacle plate.

[2] To reduce smoke underground, at first coke was burnt, changed in 1869 to smokeless Welsh coal.

These were supplied with a tender capacity of 67 cubic feet (1.9 m3); after 1868 the boiler pressure had been increased to 130 psi (900 kPa).

[citation needed] When five Burnett 0-6-0 tank locomotives were received in 1868 for the St John's Wood Railway, they took the numbers 34-38, so the A Class consisted of Nos.

[13] Originally, the locomotives were bright olive green lined in black and yellow.

The following British companies owned and operated these tank engines, either from new or second hand from the Metropolitan (Excluding the District-owned machines):[15] - Sir Arthur Elvin is reported as purchasing two from the Metropolitan Railway for £190 each.

[This paragraph needs citation(s)] In 1877, the New South Wales Government Railways (NSWGR) ordered 34 locomotives with tenders based on this design from Beyer Peacock.