The British Rail Class 28 (Metro-Vick Type 2) diesel-electric locomotives, known variously as 'Metrovicks', 'Crossleys' or 'Co-Bos', were built under the Pilot Scheme for diesel locomotives as part of the British Railways 1955 Modernisation Plan.

These Crossley-engined locomotives were one of two designs built under the Pilot Scheme to use two-stroke diesel engines, the other being the Class 23 'Baby Deltic' locomotives.

The locomotives had a Co-Bo wheel arrangement (a 6-wheel bogie at one end, a 4-wheel bogie at the other) – unique in British Railways practice and uncommon in other countries, although Japan also used some C-B diesel hydraulics. The maximum tractive effort of 50,000 lbf (220 kN) was unusually high for a Type 2 locomotive but, as there were five (not four) driving axles, the risk of wheelslip was minimal.