A locomotive, also known as a train engine, is a type of vehicle that provides the power for a train. The two most common types of locomotives are STEAM and DIESEL. STEAM locomotives use STEAM engines to generate power, while DIESEL locomotives use DIESEL engines. STEAM locomotives have been around since the early 19th century, while DIESEL locomotives were first developed in the 1920s. Both types of locomotives are still used today, although DIESEL locomotives are more common.