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 boiler and firebox were also moved back, thus resulting in a shortened cab. The London and North Eastern Railway classified them both as J6. Initially, there was to be 120 members of this class. However, an order of ten was canceled so that Doncaster Works could build ten of Gresley's N2 Class 0-6-2 Tanks, which shared the same cylinders, boilers, valve gear, and piston valves as the J6s. The J6s had superheaters and piston valves operated by Stephenson valve gear. The class earned the nickname "Knick-Knacks" due to the sound made by the locomotives when steam was shut off. Operational History Under GNR ownership, the fast goods work of the 521s and 536s was short-lived, as the arrival of the H2 Class Moguls in 1913 saw the class reassigned to lighter goods and occasional passenger traffic. The class was also used on coal trains between Colwick and Hornsey. All survived into LNER ownership in 1923, being reclassified as J6s. The LNER put the class to good use, with about twenty locomotives being allocated to the former Great Central network in 1923. These worked alongside the J10 Class and the J11 Class "Pom-Poms", with common duties for them being beer trains out of Burton, heavy coal trains, and excursions along the Lincolnshire coast. On multiple occasions, the class would go as fast as 66 mph (106.22 km/h). This is what led to them also being used on timed cross-country passenger trains from Grantham to Derby via Nottingham. Seven members of the class were reallocated to the North East during World War II. This was to replace the forty J25s that were temporarily reallocated to the Great Western Railway. Some would also be temporarily based at Haymarket and around Newcastle. BR Days All 110 locomotives passed to British Railways in 1948 and had 60000 added to their numbers. The arrival of the Thompson L1 Class Adriatic Tanks led to the J6s being taken off the Grantham to Derby services.