GT3 was a prototype mainline gas turbine locomotive built in 1961 by English Electric at its Vulcan Foundry in Newton-le-Willows to investigate the use of its gas turbines in rail traction applications. It followed 18000 and 18100 as gas turbines 1 and 2. It was designed by English Electric engineer J. O. P. Hughes in a project that started in the early 1950s. Externally it resembled a steam tender locomotive, but the tender carried kerosene fuel. The designer said the traditional chassis and mechanical transmission avoided complications with relatively untried technologies for bogies and electrical transmission.

A gas turbine locomotive is a type of railway locomotive in which the prime mover is a gas turbine. Several types of gas turbine locomotive have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels (drivers). A gas turbine train typically consists of two power cars, and one or more intermediate passenger cars.