To haul heavy coal trains from Peterborough to London, Ivatt developed the class K, which was soon dubbed the “Long Tom” because of its longer boiler compared to the six-coupled locomotives. The dimensions of this boiler roughly corresponded to the class 990 or C1 (small boiler) Atlantics. It could generate enough power to haul 60 full wagons of coal. This corresponded to a train weight of 1,052 tons compared to 681 tons for the older, six-coupled freight locomotives. With the cylinder dimensions required for this, it was still possible to arrange the cylinders within the frame. From 1901 a total of 55 engines were built.
Although the engines could handle the required train weights without any problems, a high coal consumption was noticeable. Therefore, from 1908 almost all engines were superheated, with two different variants being created. The first one, later designated by the LNER as the Q1s class, retained the original cylinder dimensions and slide valves. The others, which later became LNER class Q2, used cylinders with a diameter of 21 instead of 20 inches and piston valves instead of slide valves. Both variants had Schmidt-type superheaters and both had the fully automatic Klinger-type lubrication required for superheated operation.
In 1913 number 445 was fitted with the Doncaster superheater developed by Gresley. No other engines with this superheater followed. From 1923, it was listed as class Q3 by the LNER due to its different power characteristics. In 1914, number 420 was fitted with a significantly larger boiler. Since the other boilers of this type were finally used for the 2-6-0 machines of class K2, the 420 remained a one-off.
In the 1920's the superheaters were replaced with the Robinson type which were standard on the LNER. With the introduction of the 2-8-0 locomotives of classes O1 and O2, the locomotives were no longer needed for transporting coal to London and were increasingly used in more northerly areas. During this time they were nicknamed “Sea Pigs” because of their high water consumption compared to other locomotives. From 1926 the retirement began, whereby the few locomotives with saturated boilers were affected first. By 1935 all Q1s and Q2s were gone and the only Q3 lasted until 1937.
