The LSWR 415 class is a 4-4-2T steam tank locomotive, with the trailing wheels forming the basis of its "Radial Tank" moniker. It was designed by William Adams and introduced in 1882 for service on the London and South Western Railway (LSWR).

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-4-2 represents a configuration of a four-wheeled leading bogie, four powered and coupled driving wheels, and two trailing wheels supporting part of the weight of the boiler and firebox. This allows a larger firebox and boiler than the 4-4-0 configuration.