They were highly unusual for broad gauge locomotives in having outside cylinders.
The outside cylinders drive the third axle, the inside one drives the second.
They had outside cylinders and were operational from 1913 to 1975.
On engines with outside cylinders there are three possible variations:
These were the first engines to have an outside frame with outside cylinders.
As built, the outside cylinders were situated between the leading and driving wheels.
She had outside cylinders 13in x 24in and 4 ft 0in driving wheels.
Walschaerts gear is usually used for the two outside cylinders.
As a result the outside cylinders were placed behind the front bogie with the inside cylinder well forward.
Due to space restrictions, the middle cylinder could not be parallel with the outside cylinders.