The class were a development of Kirtley’s earlier M and M2 classes intended for the London-Dover boat trains. They proved to be moderately successful for these tasks but soon needed to superseded on the heaviest trains by the larger M3 class The locomotives passed to the South Eastern and Chatham Railway in 1899 and were considered to be sufficiently useful to be worth re-boilering between 1898 and 1903.[2] The class began to be withdrawn and scrapped from 1912
Only one example survived into Southern Railway ownership in 1923, but was withdrawn almost immediately thereafter.