GER Class A55 Decapod

The GER Class A55 Decapod was a unique 0-10-0 side-tank locomotive designed by James Holden, Locomotive Superintendent of the Great Eastern Railway from 1885 to 1907, and built at Stratford Works in 1902. The Decapod — named from the Greek for ten feet, referring to its ten coupled wheels — was built to win a bet: a group of GER directors had challenged Holden to demonstrate that a steam locomotive could accelerate a train of 300 tons from rest to 30 mph in 30 seconds, matching the theoretical performance of a proposed electric railway. Holden built the Decapod to prove the point.

The locomotive was a technical tour de force. Holden's solution was to build a ten-coupled 0-10-0 tank engine with three cylinders — an unusual arrangement for British practice of the period — designed to produce the maximum possible tractive effort at low speeds for standing-start acceleration. On trials at Chadwell Heath in 1902, the Decapod hauled a train of 300 tons from rest to 30 mph in 30 seconds, meeting the challenge exactly. The electric railway proposal was abandoned.

Having served its demonstrative purpose, the Decapod was found to be impractical for regular service. Its ten coupled wheels caused severe track disturbance at anything above very low speeds — the very quality that made it effective at acceleration was a liability in normal running — and the rigid ten-wheel coupled wheelbase was incompatible with the curved track that abounded on the GER network. Holden rebuilt the locomotive in 1906 as a more conventional 0-8-0 tender engine, the Class T19 rebuild, in which form it gave ordinary service. The Decapod's original ten-coupled form was therefore short-lived, but its place in railway history as the locomotive that effectively killed a premature electric railway proposal is secure. No example of the original form was preserved, but the story survives as one of the more remarkable episodes in Edwardian locomotive engineering.