The Great Western Railway 4900 Class or Hall Class is a class of 4-6-0 mixed traffic steam locomotives designed by Charles Collett. A total of 259 were built, numbered 4900 - 4999, 5900 - 5999 and 6900 - 6958. The LMS Stanier Class 5 4-6-0 and LNER Thompson Class B1 both drew heavily on design features of the Hall Class. After nationalisation in 1948, British Railways gave them the power classification 5MT.

In what amounted to a trial run the first 14 were despatched to the arduous proving grounds of the Cornish main line. However they were so successful here and elsewhere on the GW system that by the time the first production batch of 80 had been completed in 1930 a further 178 were on order. By 1935, 150 were in service and the 259th and last Hall, No. 6958 Oxburgh Hall, was delivered in 1943.

All but one of the original Collett Halls entered British Railways service in 1948, the exception being No. 4911 Bowden Hall which took a direct hit during a bombing raid on the Plymouth area in April 1941 and was broken up. Official withdrawals began in 1959 with the prototype Saint Martin. Its accumulated mileage, both in its original form and rebuilt form, was a remarkable 2,092,500 miles.