Great Western Railway (GWR) 6000 Class King George V is a preserved British steam locomotive.

[1] Collett successfully argued with the GWR's General Manager, Sir Felix Pole, that had the axle-loading restriction of 19.5 long tons (19,800 kg) of the "Castle" class been increased to the maximum allowable of 22.5 long tons (22,900 kg), an even more powerful locomotive could have been created.

[1] Collett designed the "King" Class to the maximum dimensions of the original GWR 7 ft 1⁄4 in (2,140 mm) broad-gauge engineering used to develop its mainline,[1] resulting in the largest loading gauge of all the pre-nationalisation railways in the UK, with a maximum height allowance of 13 feet 5 inches (4.09 m).

This combination allowed the "King" class to pull the now required higher-weight 13+ coach express trains from London to Bristol and onwards to the West Country, at a higher-speed timetable average than the "Castle".

The bell carries the inscription: Locomotive King George V by the Baltimore and Ohio Railroad Company in commemoration of its centenary celebration 24 September – 15 October 1927 After returning from the US it was allocated to Old Oak Common.

Its restoration to main line service and subsequent operation is often credited with opening the door for the return of steam to the mainlines of the UK.

The engine took part in the GWR150 celebrations in 1985 hauling railtours, one trip which took place on 7 Apr was "The Great Western Limited" which was running from London Paddington to Plymouth via Bristol was booked to be worked by No.

In addition, the higher ballast beds in place on the Western Region since the early 1980s, to allow for the high speed running of the InterCity 125 train sets, have greatly reduced the running-level loading gauge of the former GWR mainline – especially under bridges – to 13 feet 1 inch (3.99 m), so enabling mainline running of a "King" class now requires a reduction in the height of the original GWR-built chimney, cab and safety valve bonnets by 4 inches (100 mm), as had been done on the restoration of King Edward I.