MTB 331 was a Coastal Motor Boat used by the Royal Navy and built by Thornycroft, a British shipbuilding firm founded by John Isaac Thornycroft.
MTB 331 Royal Navy Operator: Name: Builder: Thornycroft MTB 331, owned by Hampshire County Council and on-loan to the British Military Powerboat Trust (BMPT) at Marchwood, is the sole surviving 55' CMB. John I. Thornycroft & Company Limited, usually known simply as Thornycroft was a British shipbuilding firm founded by John Isaac Thornycroft in Chiswick in 1866. 
