There were only three locomotives, designed by Anatole Mallet (yes, that Mallet, the man who introduced an articulated compound system that had a rear rigid chassis carrying two high-pressure cylinders, and an articulated front driving truck with two low-pressure cylinders) and manufactured by the Hunslet Company of Leeds, in Britain. Nos 1 and 2 left the Hunslet works on 10th October, 1887, and No 3 followed a week later.
One of the more radical features was the use the twin boilers, one each side of the central rail. While this was a less than desirable scheme, involving the duplication of many parts, it is hard to see how else the weight of the locomotive could have been balanced. The two boilers were linked by water and steam pipes to keep the water levels equal.