20 units of the GWR 4500 Class, which were designed as small mixed traffic locomotives based on the earlier 4400 Class and can reach the speed of 60 miles per hour, were built in 1924, during Collett's tenure at Swindon.
They were designed as small mixed traffic locomotives, mainly used on branch lines. The design was based on the earlier 4400 Class, but with larger driving wheels and altered wheel spacing. This gave them extra speed  capable of 60 mph (97 km/h) in service. A total of 75 were built; 55 were built in four batches between 1906 and 1915 and a fifth batch of 20 locos was built in 1924, during Collett's tenure at Swindon. 
