Founded as Ally & MacLellan, Glasgow in 1875 and then later known as the Sentinel Waggon Works Ltd, the company went through various place and name changes until in 1957 Sentinel (Shrewsbury) Ltd was obtained by Rolls-Royce. At that time Sentinel were producing steam locomotives and lorries, but the manufacturing of these vehicles ceased in 1958. In 1959 Sentinel produced a prototype diesel shunter which was operated on the military controlled Shropshire & Montgomeryshire Railway.
In total 17 were produced and operated quite successfully during that year. 1963 saw the introduction of the 34 ton chain drive 4 wheel Rolls-Royce diesel powered Sentinel shunter rated at 233 bhp which was later uprated to 255bhp. As time progressed the design was modified with all manner of variations, including 6 and 8 wheel coupled locomotives which found service in collieries, dockyards, quarries and foundries, with others being exported and operated on Portuguese Railways. Over the years, as these locomotives were retired, many found their way on to preserved railways where they continue to provide stalwart service.