The A1 Terrier was built at the Brighton Works under the design of William Stroudley in 1872, and between 1874 and 1880 were primarily employed on London suburban services operated by the LB&SCR. As the demands placed on the commuter network increased, the A1 Terriers were replaced by heavier more powerful tank engines and then sold to other private operators to work on branch line and shunting operations.
Sixteen of the class were modified between 1911 and 1913 and again in 1919 with a new boiler and extended smokebox plus some other improvements and were classified A1X. The Class survived well into nationalisation with the final Terrier being decommissioned in 1963. In all 10 Terriers survived into preservation.