The A12 locomotives of the London and South Western Railway were built between the years 1887 and 1895 to the design of William Adams.

The 90 members of the class were built in batches, as shown in the following table.

All 90 passed to the Southern Railway in 1923, following the introduction of the Grouping Act.

The four operated by British Railways were all withdrawn in its first year (1948), excluding DS3191 which was used for steam supply at Eastleigh Works and lasted until 1951.

This article relating to steam locomotives operated in England is a stub.