Coastal motor boat

|hide_header= |header_caption= |length= o/a |displacement= |propulsion=One shaft; various choices of petrol engine |notes=Mahogany plank on frame construction; single-step planing round-form hull |armament=* 1 × torpedo * 2–4 × Lewis guns * Depth charges or mines |complement=2–3 }} }} In 1910, Thornycroft had designed and built a speedboat called Miranda IV. She was a single-step hydroplane powered by a Thornycroft petrol engine and could reach . A boat based on 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 18-inch torpedo. 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. The restriction on weight meant 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. A trip-wire between the torpedo and the ram head would start the torpedo motors once pulled taut during release. The CMB would then turn hard over and get out of its path. 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. ==55-foot Coastal Motor Boats==

| hide_header = | header_caption = | displacement = | length = o/a | beam = | draught = | propulsion =* total power depending on engines * Two shafts | speed = | crew = 3–5 | notes = | armament =* 2 × torpedoes or 1 × 18-inch torpedo plus four depth charges * 4 × Lewis guns }} }} Larger versions of the 40-footer were ordered in 1916. Speeds from were possible, depending on the various petrol engines fitted. At least two unexplained losses due to fires in port are thought to have been caused by a build-up of petrol vapour igniting. | name = 55-foot CMBT (1941 class) | operators = | total_ships_completed = 14 | total_ships_preserved = 1 (MTB 331) }} | hide_header = | header_caption = | displacement = | length = | beam = | draught = | propulsion =* 2 × Thornycroft RY12 petrol engines * Two shafts | speed = | crew = | notes = Mahogany plank on frame construction; single-step planing round-form hull | armament =* 2 × torpedoes * Depth charges or mines }} }} The design was so successful that more were built during World War II. The last survivor, MTB 331, is of this group, built in 1941. ==70-foot Coastal Motor Boats==

Twelve 72 ft long CMBs were ordered in early 1918 for minelaying (7 magnetic mines) or torpedo work (6 torpedoes). Five were cancelled; of the remainder, 3 survived the Second World War, with CMB 103 MT, built by Camper and Nicholsons in 1920, preserved as a museum ship. She was restored in August 2011 and is on display at The Historic Dockyard Chatham. ==Service history==

In December 1916, the 3rd Coastal Motor Boat Division proceeded to Dunkirk under the command of Lieutenant W. N. T. Beckett commanding and operated on the Belgian coast. On 7 April 1917, the 3rd CMB Division attacked a group of German destroyers anchored at Zeebrugge. As a result, one destroyer was sunk and one very seriously damaged. For these actions Beckett was mentioned in Despatches and was awarded the Distinguished Service Cross (DSC). During the Zeebrugge Raid on 23 April 1918 to block the port, Coastal Motor Boats and Motor Launches were fitted out to deploy a smoke screen. Sixteen Coastal Motor Boats were lost during the war. In 1919 the British operated against Soviet Red forces in the Baltic. Coastal Motor Boats were initially used for secret duties to move agents in and out of Soviet Russia from a base in Finland. But in June 1919, the commander of the force, Lieutenant Augustus Agar, took two CMBs in a raid on Bolsheviks' ships in Kronstadt. Agar, in Coastal Motor Boat 4, entered the harbour and sank the cruiser . Agar was awarded the Victoria Cross for his part in this operation. In August, a larger operation supported with aircraft managed to damage one battleship and sink a depot ship. There were casualties as the mission came under heavy fire. For piloting the boats there Lt. Agar was awarded a Distinguished Service Order to accompany his Victoria Cross. Gordon Charles Steele (Coastal Motor Boat 88) and Claude Congreve Dobson (Flotilla commander in the 55 ft Coastal Motor Boat 31) received Victoria Crosses. Russell Hamilton McBean (commander of CMB 31), Edward Bodley (CMB 72) and Francis Yates received DSOs. In January 1919 a force of 12 CMBs was dispatched to the Caspian Sea (travelling by rail from Batumi on the Black Sea coast to Baku) to join a British naval unit supporting the anti-Bolshevik governments of the Republic of Armenia, Azerbaijan Democratic Republic and the Democratic Republic of Georgia. == Survivors ==

The hull of CMB 4 in which Augustus Agar won his VC for the attack on Kronstadt naval base in 1919 and sank the cruiser Oleg was, for many years, at the Vosper Thornycroft works on Platt's Eyot on the Thames near Kingston. When these works closed it was restored and can now be seen in Boathouse 4 at Portsmouth Historic Dockyard where it is on loan from the Imperial War Museum Duxford with details of these boats and the action. Agar's VC is at the Imperial War Museum in London. The hull of the other remaining example, CMB 9, is identical to that of CMB 4, for many years thought to be the sole survivor of the type. Her crew consisted of Archibald Dayrell Reed and Lieutenant Harold Drew. CMB 9 was converted to a Distance Control Boat in 1917, the first CMB so converted and in so doing became DCB 1. The DCB role was and still is in part classified, completely autonomous, unmanned and radio controlled via aircraft, therefore can considered to be the first autonomous drone vessel. Following the success of the Royal Flying Corps drone 'Aerial Target' aircraft trials in March 1917, A. M. Low's Experimental Works at Feltham adapted their radio control system, enabling two DCB craft to be controlled from one aircraft and proving in the 1918 trials that a flotilla of up to eight DCBs could be controlled in close formation. At the conclusion of extensive post war trials CMB 9 / DCB 1 was converted back to her original condition, remaining in service until 1950. She has been restored in her role as CMB 9 and is based at Avonmouth and took part in the 2014 Remembrance Day events in Bristol. The boat is listed on the register of National Historic Ships, certificate no 2430. MTB 331, owned by Hampshire County Council and on-loan to the British Military Powerboat Trust (BMPT) at Marchwood, is the sole surviving 55-foot CMB. Built in 1941, the penultimate 55-foot built, her design was based on that of the 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. ==See also==