The Great Northern Railway Class H4 (classified K3 by the LNER) was a class of 2-6-0 steam locomotive designed for mixed-traffic work.The type was a more powerful development of the earlier H3 (LNER K2) class and was notable at the time, as the 6-foot-diameter (1.8 m) boilers were the largest fitted to any British locomotive to that date. After formation of the London and North Eastern Railway, the type became known as class K3 and was adopted as an LNER standard design.