BoCo is a mixed traffic diesel engine.
BoCo is painted in a lighter shade of green with yellow warning panels, The number D5702 is painted on his sides in white.
BoCo is based on a BR Class 28 Co-Bo diesel-electric engine. His name is derived from his Co-Bo wheel arrangement, though reversed as the Reverend W. Awdry thought "BoCo" sounded more affectionate. These engines were initially used on the "Condor" express freight services but the class's Crossley engines quickly proved problematic. They suffered frequent failures, and in 1961 the entire class was handed back to the manufacturer for remedial work on the engines, and to cure problems with cab windows falling out while running. Upon return to service in 1962, all members of the class were allocated to Barrow-in-Furness. The real engines were so unfortunate, and most were withdrawn and scrapped by 1969. BoCo's number is that of a real Class 28. The real D5702 was built in October 1958 and was withdrawn in September 1968, before being scrapped at J. Cashmore Scrapyards the following year.