In 1985 what may in retrospect be viewed as the harbinger of private rail operation occurred when the quarry company Foster Yeoman bought a small number of extremely powerful 3600 hp locomotives from General Motors' Electro-Motive Diesel division (GM-EMD), designated Class 59, to operate mineral trains from their quarry in Wiltshire. Although owned and maintained by Foster Yeoman, the Class 59s were manned by British Rail staff. During acceptance trials, on 16 February 1986 locomotive 59001 hauled a train weighing 4639 tonnes – the heaviest load ever hauled by a single non-articulated traction unit. Foster Yeoman's class 59s proved extremely reliable, and it was not long before quarry company ARC and privatised power generator National Power also bought small numbers of Class 59s to haul their own trains.