From 1879, more locomotives were needed, and the design was updated and a total of twenty-four of these later locomotives were delivered between 1879 and 1885. Originally the locomotives were painted bright olive green lined in black and yellow, chimneys were copper capped with the locomotive number in brass figures at the front and domes were polished brass. In 1885, the colour changed to a dark red known as Midcared, and this was to remain the standard colour and taken up as the colour for the Metropolitan line by London Transport in 1933. When in 1925 the Met classified its locomotives by letters of the alphabet, these were assigned A Class and B Class. When the M&SJWR was being built, it was considered that the Class A and B tanks would struggle on the gradients and five Worcester Engine 0-6-0 tank locomotives were delivered in 1868. However, it was soon found that the Class A and B locomotives could manage trains without difficulty and the 0-6-0Ts were sold to the Taff Vale Railway in 1873 and 1875.
