What is the real-life locomotive class of Gordon?

Gordon is based on the LNER Class A1 Pacific locomotive. In The Railway Series and its television adaptation, he is the large blue express engine of the North Western Railway, a role inspired by Britain’s powerful 4-6-2 Pacific locomotives.

Gordon’s fictional history also connects him with the Flying Scotsman, who is described as his brother. The real locomotive design associated with Gordon is the original Gresley A1 class, developed by the London and North Eastern Railway for fast express passenger services. Several A1 locomotives were later rebuilt into A3s, which is why Gordon is sometimes loosely identified with the A3 family.

A common mix-up is confusing Gordon with an LNER A4, the streamlined class that included Mallard. The A4s were a separate, later design with distinctive streamlined casings. Gordon’s appearance and story instead point to the earlier A1 Pacific type, even though the franchise’s fictional engineering details are not perfectly consistent across books and screen versions.