The take over of Sentinel (Shrewsbury) Ltd by Rolls-Royce Ltd in 1956 for the manufacture of the Rolls-Royce diesel engines put the future locomotive production of any sort at Shrewsbury in doubt. Rolls-Royce had agreed to complete the steam locos on order, and four steam receiver locos ordered by Dorman Long in 1956, but only after much discuss did Rolls-Royce decide in 1957 to design and build a diesel locomotive of similar weight and power to the 200 hp steam locomotive. THR would assist in the design and development of these diesel machines and become the sole distributor.