The N15 class was designed by Robert W Urie for the London & South Western Railway but only 20 of the 74 that eventually made up the class were built by him at Eastleigh. These had Urie's stove pipe chimney and a Drummond style cab. The N15 was styled on the H15 Class and we have yet to see one of these early versions from Hornby - although no doubt at least one will come.

None of the class were named until the Southern Railway, seeking better publicity, started naming its locomotives. In charge of publicity, John Elliot came up with the idea of adopting the names from the King Arthur fables. These were applied in the mid 1920s. This explains why the name 'King Arthur' was not applied to one of the first batch built.

In taking over as CME of the Southern Railway at Grouping in 1923, Richard Maunsell made slight alterations to the design, to make the class significantly more powerful, before building a further 10 locomotives at Eastleigh. On the models we see the change to the valve gear, chimney and the addition of external high-pressure steam pipes to the cylinders (although the latter are mostly hidden by smoke deflectors fitted from 1927). 30 engines were also ordered from the North British Locomotive Company in Scotland and these were nicknamed 'Scotch Arthurs'. On the models these can be identified by a more rounded cab roof which also extends further back to give greater protection for the crew. A final batch of 14 Class N15s was built at Eastleigh and were fitted with Ashford six-wheeled 3,500 gallon tenders.