Coming from a railway company with a well-developed standardisation policy, the 15xx was an unconventional break. Unlike almost all previous panniers they had outside cylinders,
Walschaerts valve gear, and a very short
wheelbase of to go round curves of . Above
footplate level they were very similar to the
9400 class, and shared the same Standard No. 10 boiler. The major difference was below the (very small)
footplate, where they resembled the
USATC S100 Class that the GWR and other railways had used during the Second World War. Although a functional design, the class had limited usefulness as they were route-restricted by their high weight and were unsuitable for fast running because of their short wheelbase. Largely confined to empty stock workings at
London Paddington station, their lives were short; for example 1509 lasted barely ten years in BR service. Four of the class, 1506 to 1509, were based in Wales, Newport Pill, Ebbw Junction & Cardiff Canton, 1508 was withdrawn from that last shed. Like the
1600 and 9400 classes, their construction now appears to have been of doubtful value. The onset of
dieselisation and the decline in traffic on the railway network meant the 1500s were withdrawn and scrapped while still in workable condition. However No. 1501 has seen regular use at the
Severn Valley Railway in preservation, much longer than its life in BR ownership. ==Preservation==