||This article relies largely or entirely upon a single source. (December 2014)
The Great Northern Railway 521 Class was a class of 0-6-0 steam locomotives, introduced in 1911. They were designed by Henry Ivatt for goods traffic. From 1912 to 1922 further examples, slightly modified by Nigel Gresley, were built and designated 536 Class. The most obvious difference was in the front sandboxes. These were below the running plate on the 521 but above it, and merged with the front splashers, on the 536. The London and North Eastern Railway classified them both as J6. These locomotives had superheaters and piston valves operated by Stephenson valve gear.
One hundred and ten locomotives passed to British Railways in 1948 and they were numbered 64170-64279. The J6s were withdrawn between 1955 and 1962 and none have been preserved.
Detail drawings and scale model kits are available from some suppliers.
- Ian Allan ABC of British Railways Locomotives, 1948 edition, part 4, page 28.