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Type: 55ft CMBT
Service: Royal Navy
Builders: Thornycroft, Hampton.
Year Built: 1941
Number Built: 14
Displacement: 17.0 Tons
Length: 60 ft
Beam: 11½ ft
Draught: 4ft
Hull: Mahogany
Engines: 2x 650hp Thornycroft RY12.
Max Speed: 40 knots

MTB 331, owned by Hampshire County Council (HCC), which is now on loan to the British Military Powerboat Trust (BMPT) at Marchwood, is the sole surviving 55ft Thornycroft stepped hull motor torpedo boat, and as such is quite unique. Built in 1941, and the Royal Navy's penultimate 55ft Thornycroft hydroplane, her design was based on that of the Coastal Motor Boats (CMBs) of 1916.

During World War 1 of 1914-18, following a suggestion from three officers of the Harwich destroyer force that small motor boats carrying a torpedo might be capable of traveling over the protective minefields and attacking ships of the German Navy at anchor in their bases, the Admiralty gave tentative approval to the idea and, in the summer of 1915, produced a Staff Requirement. This was for a boat which, complete with an 18 inch torpedo, should not exceed the weight of the 30 foot motor boat then carried in the davits of a light cruiser, namely 4.5 tons. The speed of the boat when frilly loaded, was to be at least 30 knots and sufficient fuel was to be carried to give a considerable radius of action.

Several companies were approached, but only one, John I Thornycroft & Co Ltd, considered it possible to meet such a requirement. In January 1916 after producing, in association with the Admiralty, a suitable design, Thornycroft received orders for twelve boats, the last of which was completed in August 1916. The restriction on weight meant that the torpedo had to be carried and fired by unconventional means. Instead of using a heavy torpedo tube and firing the torpedo by compressed air or a cordite charge, the torpedo was carried on rails in a trough, built into the after part of the boat's hull, and fired backwards, tail first, by means of a long steel ram, operated by a cordite cartridge. As the 1914-18 War continued, further CMBs were ordered. These included in April 1917, 55 foot boats which, powered by two engines and displacing about 11 tons, were capable of carrying two 18 inch torpedoes in a trough aft.

After 1918 there was no further Admiralty order for Thornycroft "CMB Type" MTBs, however between September 1939 and August 1941, fourteen 55 foot boats of this type, originally ordered for foreign navies, were requisitioned by the Admiralty. MTB 327 to 331, ordered on 12 June 1940 for the Philippines, were replacements for MTB 213-217, requisitioned by the Admiralty earlier that month. Taken over in August 1941, while still under construction, they were completed between June and October 1941. They commissioned on 3 November 1941 and with MTB 345 formed the 12th MTB Flotilla. They arrived at HMS Hornet, Portsmouth on 11th November 1941, were still there on the 24 November, but were at Dartmouth by 4 December where they commenced working up. After only a few weeks in commission, on 10 January 1942, they were instructed to pay of and lay up in Gunboat Yard, Haslar at one months notice. MTB 330 and 331 both recommissioned at HMS Hornet in August 1944 and paid off early the following month. It is assumed they were brought forward from Reserve to replace CMB 103 and MTB 344, which both paid off in July 1944, following service off the Normandy beaches during the Allied landings. Apart from MTB 330 and 331 recommissioning for these short periods in 1944, MTB 327 - 331 remained in Reserve in the sheds at Gunboat Yard, Haslar. In May 1945 all five were placed on the Disposal List and later sold by DSCD.

No information regarding the post war history has come to light, and nothing is known of MTB 331's history prior to May 1951 when MTB 331 was registered at Teignmouth, as the JONREY, Official No. 183954, and was listed in Lloyd's Yachts from 1953 until 1973. During this period she had 4 registered owners, the last being Mr Bowmen of Bristol. There is evidence from around 1972 which shows the JONREY in the Cumberland Basin at Bristol with a caption which indicated that she was to be restored to her wartime appearance. By 1980, if not earlier, Mr Robert G Morley of Bristol became the owner of JONREY, and remained so until she was acquired by Hampshire County Council (HCC), about ten years later.

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