Vincent Raven had been appointed Chief Mechanical Engineer of the North Eastern Railway (NER) in June 1910.

His predecessor, Wilson Worsdell, had introduced three-cylinder simple-expansion locomotives to the NER with the Class X 4-8-0T, ten of which were built in 1909–10 for heavy shunting.

One of Raven's first designs was another three-cylinder locomotive, the Class Y 4-6-2T, twenty of which were built in 1910–11 for hauling coal trains from collieries to ports.

[1] Worsdell's two-cylinder Class V 4-4-2 were handling the principal East Coast expresses, and Raven combined the 4-4-2 wheel arrangement with three cylinders to produce his new design.

[2] Originally classified NER Class V2, the first 20 were built in 1911 by the North British Locomotive Company.

[3][4] At the end of 1920, the fifty locomotives were based at principal main-line depots: there were 21 at Gateshead, fourteen at York, seven at Tweedmouth, five at Heaton, and three at Leeds (Neville Hill).

At these depots they shared duties with the other NER Atlantics, classes V and 4CC: these included the principal expresses on the East Coast Main Line: York–Newcastle and Newcastle–Edinburgh, together with the through services from Liverpool (Lime Street) to Newcastle, which were hauled by a locomotive of the London and North Western Railway between Leeds and Liverpool.

[4] To begin with, they continued on the same duties, but in 1924–25, the LNER took delivery of forty Class A1 4-6-2, of which ten were allocated to Gateshead and five each to Haymarket and Heaton.

However, the cylinder bore and boiler pressure of the superheated locomotives were altered to match those of the first ten.

[10] Normally, a locomotive boiler is fed with cold water from the tender or tank and must be heated from ambient temperature to its boiling point in order to make steam.

Some engineers had tried different systems for extracting heat from the exhaust steam in order to pre-heat the boiler feedwater, and so use less fuel in the firebox.

A heat exchanger was mounted on the left-hand side of the locomotive above the footplate, through which exhaust steam was passed.

There were some concerns about engaging the booster at higher speeds, however the unitary 1:1 gearing was considered to make this easier.

The growing amount of Gresley A1s, A3s and A4s made the experiment redundant (seeing the A4s were scheduled to climb Cockburnspath hauling a 312 tons load at an average speed of 55 mph [89 km/h]).

The modifications required a new crank axle and new bogie having smaller wheels, which was mounted further forwards.

2212 (the former Uniflow locomotive) was similarly modified, except that the valve gear allowed seven different settings for forward running, and two for reverse.