This is a BR Modernisation Plan "Type 2" design by the Birmingham Railway Carriage & Wagon Co. of Smethwick. A total of 116 locomotives were built. The first batch of 47 locomotives, delivered in 1958 and 1959, had Sulzer engines capable of 1,160 b.h.p. They were under-powered for some duties, and later locomotives had uprated engines which could produce 1,250 b.h.p. Under later categorised by TOPS, the 1958/59 locomotives were identified as Class 26, and those with the more powerful engines, which built in 1961/62, became Class 27.
No 27001, originally numbered D5347, was the first of the more powerful locomotives, and was delivered in June 1961 to Thornton Junction shed in Fife. Scotland received 22 of these locomotives as new, most going to Eastfield shed in Glasgow. As they were intended for mixed traffic duties, they were fitted with boilers to supply steam to carriage heating systems, at a time when steam locomotives remained in service. At Eastfield, they replaced troublesome North British Locomotive Company built diesels on duties such as the West Highland services. The locomotives supplied new to Scotland were fitted with tablet catchers.
Eighteen members of the class were modified in the early 1970s, and were used on the Scottish Region flagship Edinburgh - Glasgow service, replacing Inter-City DMUs until they were themselves replaced by push-pull fitted Class 47 locomotives in 1979. To achieve fast turn-round times and high utilisation, the Class 27s operated that service with a locomotive at both ends of the train.
27001 remains in "as built" condition. Significant withdrawals of Class 27 locomotives commenced in 1986, and all were out of service by the end of 1987. 27001 was withdrawn in July 1987 from Eastfield Depot.
