The Great Western Railway purchased two diesel shunters, and ordered a further seven immediately prior to Nationalisation, which were delivered to British Rail in 1948–49.
The two shunters used by the GWR were numbered 1 and 2, while a series commencing at 501 was planned for the new locomotives ordered in the 1940s.
British Rail renumbered both its inherited and new locomotives in a series commencing from 15100.
It was very similar to the London, Midland and Scottish Railway's (LMS) departmental locomotive number 2, which was built a couple of years later.
It was a 0-6-0 diesel electric shunter, very similar to the LMS 7069 class (later British Rail Class D3/6), and with a close family resemblance to the Southern Railway Maunsell 350 hp DMS (SR 1 - SR3).