5001 was an experiment by NMBS to build a 4000 HP strong diesel locomotive, capable of running 140 km/h.Commenced in 1969 the 5001-experiment (that saw 5101 extensively rebuild and reappearing in blue with white lines) flopped dramatically. In 1974, after the loco was more OFF than ON the tracks, NMBS decided to quit the 5001 saga and the loco was rebuild bac in 5101. But the 5001 never was lost in the minds of the railway fraternity in Belgium and the first masquerade saw a Class 51 as 5001 in 1991 during the 150 Anniversary of Liége-Aachen. This reappearance of 5001 was short-lived, but in 2005 TSP/PTF decided to repaint 5128 into 5001. It was hoped, that the remains of 6003 (a four-axle version of Class 51) could be saved using parts of 5117, but when in 2009 inspection revealed, that 6003 was irreparably lost, TSP/PTF decided to cancel the 6003 project and stay put to the second masquerade of 5001. At this moment, the third 5001 has spend more years being 5001 than the original one! 
Scanned photo by Leon Schrijvers  Leon2711schrijvers@yahoo.co.uk