Coastal Motor Boat
Encyclopedia
During the First World War
, following a suggestion from three junior 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 (58.8 km/h) 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 torpedo
es, depth charge
s or for laying mine
s. Secondary armament would have been provided by light machine guns, such as the Lewis gun
. Weight of a fully loaded boat, complete with 18 inches (457.2 mm) torpedo, was to not exceed the weight of the 30 feet (9.1 m) long motor boat then carried in the davit
s of a light cruiser, i.e. 4.5 tons.
The CMBs were designed by Thornycroft
, who had experience in small fast boats. Engines were not proper maritime internal combustion engines (as these were in short supply) but adapted aircraft engines from firms such as Sunbeam and Napier
.
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, following a suggestion from three junior officers of the Harwich
Harwich
Harwich is a town in Essex, England and one of the Haven ports, located on the coast with the North Sea to the east. It is in the Tendring district. Nearby places include Felixstowe to the northeast, Ipswich to the northwest, Colchester to the southwest and Clacton-on-Sea to the south...
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
German Navy
The German Navy is the navy of Germany and is part of the unified Bundeswehr .The German Navy traces its roots back to the Imperial Fleet of the revolutionary era of 1848 – 52 and more directly to the Prussian Navy, which later evolved into the Northern German Federal Navy...
at anchor in their bases, the Admiralty
Admiralty
The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...
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
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
.
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 (58.8 km/h) 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 torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...
es, depth charge
Depth charge
A depth charge is an anti-submarine warfare weapon intended to destroy or cripple a target submarine by the shock of exploding near it. Most use explosives and a fuze set to go off at a preselected depth in the ocean. Depth charges can be dropped by either surface ships, patrol aircraft, or from...
s or for laying mine
Naval mine
A naval mine is a self-contained explosive device placed in water to destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel...
s. Secondary armament would have been provided by light machine guns, such as the Lewis gun
Lewis Gun
The Lewis Gun is a World War I–era light machine gun of American design that was perfected and widely used by the British Empire. It was first used in combat in World War I, and continued in service with a number of armed forces through to the end of the Korean War...
. Weight of a fully loaded boat, complete with 18 inches (457.2 mm) torpedo, was to not exceed the weight of the 30 feet (9.1 m) long motor boat then carried in the davit
Davit
A davit is a structure, usually made of steel, which is used to lower things over an edge of a long drop off such as lowering a maintenance trapeze down a building or launching a lifeboat over the side of a ship....
s of a light cruiser, i.e. 4.5 tons.
The CMBs were designed by Thornycroft
John I. Thornycroft & Company
John I. Thornycroft & Company Limited, usually known simply as Thornycroft was a British shipbuilding firm started by John Isaac Thornycroft in the 19th century.-History:...
, who had experience in small fast boats. Engines were not proper maritime internal combustion engines (as these were in short supply) but adapted aircraft engines from firms such as Sunbeam and Napier
Napier & Son
D. Napier & Son Limited was a British engine and pre-Great War automobile manufacturer and one of the most important aircraft engine manufacturers in the early to mid-20th century...
.