Built for the Great Eastern Railway, the J68 class was introduced in 1912. A total of 30 of these little 0-6-0T's were built by the Stratford Works. In 1961 the last of the J68's was scrapped. In the case of 68640, this met the cutter's torch in 1959. None survive.
This is an axial or barrel engine, which has multiple cylinders arranged around and parallel to a central shaft, like the chambers in the cylinder of a revolver. The piston thrust is converted to rotary motion by a swashplate, wobble-plate or Z-crank mechanism.