Coastal Motor Boats
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During World War 1, following a suggestion from three officers of the Harwich destroyer force that small motor boats carrying a torpedo might be capable of travelling 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 requesting designs for a coastal motorboat for service in the North Sea.
These boats were expected to have a high speed, making use of the lightweight and powerful petrol engines then available. The speed of the boat when fully loaded was to be at least 30 knots and sufficient fuel was to be carried to give a considerable radius of action.
They were to be armed in a variety of ways, with torpedoes, depth charges or for laying mines. Secondary armament would have been provided by light machine guns, such as the Lewis gun. Weight of a fully-loaded boat, complete with 18" torpedo, was to not exceed the weight of the 30' motor boat then carried in the davits of a light cruiser, i.e. 4.5 tons.
[edit] 40' Coastal Motor Boats
| Career (UK) |  |
|---|---|
| Operator: | Royal Navy |
| Builder: | Thornycroft, Southampton |
| Launched: | 1916 |
| Class overview | |
| Name: | 40' CMB |
| Operators: | Royal Navy |
| Completed: | 39 |
| Preserved: | CMB 4, CMB 103 |
| General characteristics | |
| Length: | 40 ft (12 m) |
| Propulsion: | single screw, various choices of petrol engine |
| Armament: | single 18" torpedo, depth charges or mines |
| Notes: | Mahogany plank on frame construction, single-step planing round-form hull |
In 1910, Thornycroft had designed and built a 25' speedboat called Miranda IV. She was a single-step hydroplane powered by a 120 hp Thornycroft petrol engine and could reach 35 knots. [1]
A 40' boat based on the Miranda IV was accepted by the Admiralty for trials. A number of these boats were built and had a distinguished service history, but in hindsight they were considered to be too small to be ideal, particularly in how their payload was limited to a single torpedo, either 18".
Several companies were approached, but only Thornycroft, considered it possible to meet such a requirement. In January 1916 twelve boats were ordered, all of which were completed by August 1916. Further boats were built, to a total of 39. [2]
The restriction on weight meant that the torpedo could not be fired from a torpedo tube, but instead was carried in a rear-facing trough. On firing it was pushed backwards by a cordite firing pistol and a long steel ram, entering the water tail-first. There is no record of a CMB ever being hit by its own torpedo, but in one instance the firing pistol was triggered prematurely and the crew had a tense 20 minutes close to the enemy whilst reloading it. [3]
[edit] Service History
- Losses [4]
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- In June 1919 a force of two CMB attacked Kronstadt and sank the cruiser Oleg. Lt. Augustus Agar of CMB4 won his Victoria Cross in this operation. [3]
- In August, a larger combined operation with aircraft managed to sink two battleships and a depot ship. There were casualties as the mission came under heavy fire.[5] Lt. Agar won a DSO to accompany his VC. [6]
[edit] Survivors
- CMB 103 [7]
[edit] The 55' Coastal Motor Boats
| Career (UK) | |
|---|---|
| Name: | MTB 331 |
| Operator: | Royal Navy |
| Builder: | Thornycroft, Southampton |
| Launched: | 1941 |
| Status: | British Military Powerboat Trust, Marchwood |
| Class overview | |
| Name: | 55' CMBT |
| Operators: | Royal Navy |
| Completed: | 14 (1941 class) |
| Preserved: | MTB 331 |
| General characteristics | |
| Displacement: | 17 tons (1917 boats, 11 tons) |
| Length: | 60 ft (18 m) |
| Beam: | 11.5 ft (3.5 m) |
| Draught: | 4 ft (1.2 m) |
| Propulsion: | twin screws & twin 650hp Thornycroft RY12 petrol engines |
| Speed: | 40 knots |
| Armament: | twin 18" torpedoes, depth charges or mines |
| Notes: | Mahogany plank on frame construction, single-step planing round-form hull |
In 1917 Thornycroft produced an enlarged 55' version. This allowed a heavier payload, and now two torpedoes could be carried.
Speeds from 35 to 41 knots were possible, depending on the various petrol engines fitted. Use of petrol in a boat is always a fire risk. At least two unexplained losses due to fires in port are thought to have been caused by a build-up of petrol vapour igniting.
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Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. |
The design was so successful that more were built during World War 2. The last survivor, MTB 331, is of this group, built in 1941.
[edit] Service History
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Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. |
[edit] Survivors
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. [8] Built in 1941, the penultimate 55' built, her design was based on that of the Coastal Motor Boats (CMBs) of 1917 with two V12 engines. Her post-war history is incomplete, but she was registered as the JONREY at Teignmouth, then later at Bristol. She was acquired by the Council, around 1990. Some restoration after this was carried out at Priddy's Hard, then she was transported by road to BMPT Marchwood in March 2000. [9]
[edit] Modelling
Construction of a 1:24 scale model of a 55' torpedo boat has recently been a magazine cover article. [1]
[edit] Further Reading
- Harald Fox (1978). Fast Fighting Ships 1870-1945.
- M P Cocker (2006). Coastal Forces: Vessels of the Royal Navy from 1865. National Maritime Museum, Greenwich.
[edit] References
- ^ a b Barrie Griffin (April 2008). "The Thornycroft 55' Coastal Motor Boat". Marine Modelling International.
- ^ WW1 numbers and losses of MTB classes.
- ^ a b A naval operation in the Baltic. “sinking of the Russian Cruiser 'Oleg' in 1919”
- ^ British Minor Warship Losses - 1914 - 1918.
- ^ (1969) History of WWI Vol. 8.
- ^ The Oxford Illustrated History of the Royal Navy, page 330.
- ^ CMB 103 - 40' Coastal Motor Boat. Australian Plastic Modeller's Association (2000).
- ^ The Preservation of Thornycroft Coastal Motor Boat 331 at Fort Gilkicker. Hampshire County Museums Service (1991).
- ^ MTB 331 home site and restoration photos. British Military Powerboat Trust (BMPT).
