The Kings entered service in 1927 with a tractive effort of 40,300 lbf (179 kN), a figure matched rather than exceeded by the Cathedral proposal.
[4] Although the King's tractive effort was lowered to 39,700 lbf (176.6 kN) after their first overhaul, they still proved capable of hauling the heaviest West of England expresses without assistance.
Furthermore, at the Locomotive Exchange Trials in 1948, 6018 King Henry VI proved more sure-footed climbing out of Kings Cross, where pacific locomotives were apt to slip alarmingly.
The King's driving wheels and boiler had also been designed together to stay within the network loading gauge, a limit that may have been exceeded with the LMS Princess Royal boiler.
Postwar austerity and the precarious financial situation of the Big Four railway companies prior to nationalisation[5] may also have contributed to the decision not to proceed with a prototype locomotive of the Cathedral class.