The SECR O1 class 0-6-0 were rebuilt from the SER O class locomotives between 1900 and 1932. 

The SER O Class were designed for freight work, and were the main freight engines of the SER, and later the SECR for a number of years. However, they were displaced by the more powerful C class locomotives following the amalgamation of the SER and the LCDR in 1899.

This relegated the class to working on the numerous branch lines in Kent, on both passenger and freight work. The majority were withdrawn before the outbreak of the Second World War in 1939, and those that remained were slowly withdrawn from nationalisation onwards.

The death knell for the final few members of the class came with the Modernisation Plan of 1955, which closed down many of the branch lines they continued to serve in Kent. All members of the class had been withdrawn by 1962, and only one member of the class has survived scrapping.