The LSWR T6 class was a class of express passenger 4-4-0 steam locomotives designed for the London and South Western Railway by William Adams. Ten were constructed at Nine Elms Locomotive Works between 1885 and 1886. The class were numbered 677–686, and were a development of the X2 class, based on experience gained with the locomotives in traffic. The boiler was based on that used in the T3 class, and shared the main dimensions.