Marshall, Sons & Co. was a British agricultural machinery manufacturer founded in 1848. The company was based in the Britannia Iron Works, Gainsborough, Lincolnshire. Early production was of steam engines and agricultural machinery. Later production included diesel tractors such as the Field Marshall, Track Marshall and former Leyland wheeled tractors.

A portable engine is an engine, either a steam engine or an internal combustion engine, that sits in one place while operating, but is portable and thus can be easily moved from one work site to another. Mounted on wheels or skids, it is either towed to the work site or moves there via self-propulsion.