Editing GWR 4073 Class (section)

==Background==
The origins of this highly successful design date back to the [[GWR 4000 Class|Star Class]] of 1907 which introduced the basic 4-cylinder 4-6-0 layout with long-travel valves and [[Belpaire firebox]] that was to become characteristic of [[Great Western Railway]] (GWR) express passenger locomotives. The Star class was designed to take the top express trains on the GWR, with 61 in service by 1914, but after [[World War I]] there was a need for an improved design. To meet this need, Chief Mechanical Engineer [[George Churchward]] had in mind an enlarged Star class design with a standard No.7 boiler, as fitted to his [[GWR 4700 Class]] express freight 2-8-0.{{sfnb |le Fleming|1953 |p=H13}} However, this combination would have taken the axle load over the 20-ton limit then set by the civil engineers, and in the end, nothing came of the idea.