The Great Northern Railway Class J23 was a class of steam locomotive. They had long side tanks that came to the front of the smokebox, which sloped forwards to improve visibility and had a recess cut in to aid maintenance. Forty were built by the Great Northern Railway (GNR) between 1913 and 1922, with a further 62 being added by the London and North Eastern Railway (LNER) between 1924 and 1939. They were given the nickname "Submarines" due to their long tanks. History For shunting and local goods work, the Great Northern Railway (GNR) had traditionally used saddle-tank engines of the 0-6-0 wheel arrangement; the last of these, of GNR Class J13, having been built in 1909 to the designs of Henry Ivatt, the GNR Locomotive Superintendent. Nigel Gresley succeeded Ivatt in 1911, and soon identified a need for engines to work the short-haul coal traffic in the West Riding of Yorkshire; the nature of which required that the locomotives also be suitable for shunting. He designed a new class of engine, using side tanks instead of saddle tanks. Gresley had recently begun the rebuilding of the GNR Class L1 locomotives with larger boilers, in diameter, which left a number of diameter boilers spare. Thirty of these were used in the construction of the new goods tank engines between 1913 and 1919; when ten more were built in 1922, these again used secondhand boilers, but in diameter. On the GNR, both varieties were classified J23, but the LNER divided them into J51 with smaller boilers, and J50 with larger boilers. The LNER continued the construction of Class J50, building a further 62 up to 1939, only the first ten of which were given secondhand boilers. Class J51 were rebuilt to class J50 between 1929 and 1935. Each of the two main classes exhibited variations: locomotive brakes could be operated by vacuum or steam pressure; the driving position could be on the right- or the left-hand side of the cab; and there were three sizes of coal bunker. These variations were recognised by class subdivisions: J51/1 10 built 1913–14, 4 ft 2 in boiler, vacuum brake, right-hand drive, short bunker J51/2 20 built 1914–19, as J51/1 but long bunker J50/1 10 rebuilt 1929–35 from J51/1 with 4 ft 5 in boiler J50/2 20 built 1922–24, as J51/2 but 4 ft 5 in boiler, plus 20 rebuilt 1929–34 from J51/1 with 4