The GNR O2 was development of the O1, which initially differed almost only in the number and arrangement of the cylinders. Instead of the previous two cylinders, three smaller ones were now used to improve power transmission and smooth running. For the first time, Gresley used his special valve motion on these locomotives, in which the inner cylinder was controlled by levers from the valve gear of the outer cylinders. As a result, no additional motion was needed within the frame that would be difficult to access for maintenance. The dimensions of the boiler were left unchanged compared to the O1, but the starting tractive effort was increased by around nine percent thanks to the third cylinder.
In 1918 only one prototype could be completed, another ten with a slightly modified valve gear were ordered in 1919 and delivered in 1921. The production engines got cylinders half an inch larger and an increase in boiler pressure from 170 to 180 psi. After the grouping in 1923, the LNER ordered another 15, which, given the smaller LNER standard loading gauge, got a flatter cab with side windows, a lower chimney and a repositioned whistle. Many of the earlier engines were also rebuilt in this form in 1939 in order to be able to use them on the entire LNER network. Another 16 were delivered in 1932 and 1933 and the last 25 in 1942 and 1943.
At first the O2, like the O1 before it, mainly delivered coal to London. During the war, many also had to haul other cargo on behalf of the military. After the end of the war, most of them pulled coal and ore trains again, since they belonged to the group of “mineral engines” and were well suited for this. All 67 locomotives came to British Railways in 1948 and only the prototype was quickly retired due to its different valve gear. It was only in 1960 that the other engines were also retired, which was completed in 1963. Like most British goods locomotives, the O2 were all scrapped at the end of their service life.
