The class were an enlargement of Kirtley's earlier M1 and M2 classes intended for the London-Dover boat trains. They proved to be successful for these tasks for more than a decade. The locomotives passed to the South Eastern and Chatham Railway in 1899 after which they were superseded on the heaviest trains by the SECR D class between 1903 and 1905 and transferred to secondary duties. The class was nevertheless considered to be sufficiently useful to be worth re-boilering between 1909 and 1917.
The entire class survived into Southern Railway ownership in 1923, but the appearance of the King Arthur class on the line after 1925 meant that they had all been withdrawn and scapped by 1928.