Each locomotive was equipped with two MAN L12V18/21A diesel engines, each set to produce 1,000 hp (750 kW) at 1,445 rpm.

MAN had refined the engine design to produce 1,100 hp (820 kW) at around the time the D600 order was placed with NBL.

A press run was arranged for 17 February 1958 when D600 hauled a 340-ton train between London Paddington and Bristol Temple Meads with stops at Reading, Didcot and Swindon.

[citation needed] Swindon had a spare cab which was not used and survived long after the locos had been withdrawn before finally being sold for scrap.

[citation needed] From new the D600s wore standard BR green with a 4-inch (102 mm) light grey horizontal band between the cabs a few inches above the solebar.

As the table below shows, there was a substantial gap between delivery of D601 and D602 because NBL had to equip itself to construct the engines and transmissions for these three locomotives.

The last Class 41 unit was broken up at Barry Scrapyard, while D602-D604 were sold to Cashmore's of Newport who broke them up far sooner due to the former concentrating on easily processable wagons before locomotives.

As the fleet only lasted eight years in revenue-earning service, D601 actually spent more time in the scrapyard than it did hauling trains on the main line.

An additional run is planned for November 2020 availability comprising previously un-released number/livery variations including a weathered green example.