[3] When the Barry Railway needed more locomotives for coal trains on the Vale of Glamorgan Line, it returned to Sharp Stewart (who had also supplied most of the locos on the railway) for similar engines to the Class D. The result was the Class H 0-8-2T, which had the same small driving wheels to give a high tractive effort, and were heavy (for the time) giving good braking.
They were built as tank locomotives with an additional rear pony truck that allowed a greater coal and water capacity than that of the small Class D tender, whilst also being shorter and not requiring the use of turntables.
[1] Once delivered, however, the Class H locos were employed in hauling heavy coal trains between Barry Docks and the large yard at Cadoxton, with this task being their main duty in service.
Improvements were made to numbers 1380 and 1383 at Swindon Works, including GWR pattern safety bonnets, enlarged bunkers, new buffers and an extended smokebox.
At the same time the boiler pressure on these two locos was raised by 10 psi (69 kPa), with the tractive effort also being increased appropriately.