The NBR Class M was a class of 4-4-0 steam locomotive of the North British Railway. The class was rebuilt during the tenures of William P. Reid and Walter Chalmers from three earlier classes, the "574", "633", and "729" which had been designed by Matthew Holmes.The locomotives passed to the London and North Eastern Railway in 1923 but withdrawals began in 1931 and only seven of the class passed to British Railways in 1948.