The up to 129.6 tonne heavy, six-axle locomotives have a diesel engine with power of up to 2,420 kW (3,245 HP). A three-phase generator feeds six series connected collector traction engines which power the axles with an axle hung gearbox. The locomotives developed for the British clearance gauge have opposing, radially steered end axles. The middle axles on the other hand, can be shifted to the side for good curve performance.

The Class 66 is used across Europe in freight transport, by private railway transport companies in particular, as well as at Lappwaldbahn Cargo. These powerful locomotives are approved in Belgium, Denmark, Germany, France, the Netherlands, Norway, Luxemburg, Sweden and Romania.