the british rail class 28, originally known as metropolitan-vickers type 2, diesel locomotives were built as part of the british railways modernisation plan. the locomotives had a co-bo wheel arrangement. there was a 6-wheel bogie at one end a 4-wheel bogie at the other end. this wheel arrangement was unique in british railways practice but not uncommon in some other countries, notably japan. this affected their route availability, due to the different axle loading at each end of the loco, and made maintenance more complicated. the maximum tractive effort was unusually high for a type 2 locomotive but, as there were five (not four) driving axles, the risk of wheelslip was minimal.