The first of the T3s, No.901 was outshopped from Darlington Works in November 1919. A month later the NER organised a test train, over the Newcastle to Carlisle line, including a brake van and the company's dynamometer car to record the locomotive's performance. No.901 had 1,402 long tons (1,424 t; 1,570 short tons) in tow but handled the load with ease, registering both high power and steady acceleration. There were no problems starting on a 1 in 298 (0.335 %) grade and on the return, with a reduced load of 787 long tons (800 t; 881 short tons), the engine was untroubled by gradients as severe as 1 in 107 (0.93 %).
Despite their prowess, the original quintet of T3s was not augmented by the North Eastern Railway, a move that would have pleased footplate crews who disliked having to lubricate and maintain the centre cylinder and valve gear. Instead the enlargement of the class came under LNER. it authorised the construction of ten additional T3s and these emerged from Darlington Works during 1924.
Of the new engines two were allocated to York and a further four went to Hull. The remaining four gravitated to their natural habitat, Tyne Dock depot near South Shields. It was there eventually that all 15 T3s/Q7s congregated. Here they performed the role they were designed for. This was to haul 700-long-ton (710 t; 780-short-ton) rakes of iron orehoppers to the steelworks at Consett 1,000 ft (305 m) above sea level. On the steepest section, as severe as 1 in 35 (2.86 %) in places, one 0-8-0 pulled while another pushed.
All 15 passed into British Railways ownership in 1948 and they were numbered 63460-63474. They remained master of their task till the arrival of BR Standard Class 9F2-10-0s in the 1950s. With the loss of their bread and butter work British Railways retired all 15 of the Q7s in November and December 1962.