OO GWR 15xx Pannier Tanks

The 15xx was a rather odd design for the GWR. The 15xx was certainly a sound design for a heavy shunting engine and outside cylinders and valve gear certainly makes maintenance and preparation easier and quicker. However unlike the Southerns' purchase of USA tanks for Southampton docks the GWR had little need for powerful, short wheelbase 0-6-0 engines and the duties expected of a GWR pannier tank extended beyond shunting. The combination of short wheelbase and powerful outside cylinders made the 15xx less suitable for the fast running than the more conventional 94xx class engines.
Loco crew descriptions of the engines certainly bears out the disadvantages of the design. London crews colourfully described them has having an 'appetite for ground signals' and modern day SVR crews refer to 1501 at the 'Raging Bull', both suggesting a tendency to waddle or plunge from side to side when under power. This trait is common to powerful outside cylindered locomotives and usually countered by a leading truck providing resistance to the surging motion.
This no doubt explains (in part) British Railways' decision to order 94xx class engines to replace life-expired 0-6-0 goods engines and diesels for the shunting only duties.
Three of the class found work where they were really suitable, with the NCB at Coventry, resulting in engines 1501 being purchased for preservation on the Severn Valley Railway.