There was also the similar NS Class 500. The difference between the two classes is that Class 600 has a "6KT" diesel engine of 400 hp (300 kW) and a Knorr braking system for train use, a Class 500 has a "6K" diesel engine of 350 hp (260 kW) and only an engine brake.
The first ten locomotives of the class 500 were built for the War Department and were taken on by NS after the war after service in Europe. NS subsequently placed orders for a further 35 locomotives. There was also an order for 15 locomotives to be delivered without engines that would have an alternative engine fitted in the Netherlands. These were numbered as 451-465 briefly before being renumbered tp 701-715.
Privately owned 663 was moved from the Dartmoor Railway to the NRM annex at Shildon on 17 October 2006 to take up pilot duties. As of 2012 it has been at the Ribble Steam Railway in preston, where it first worked after repatriation in 2005. Although part way through a repaint 663 is in running order.