Limpet mine
Encyclopedia
A limpet mine is a type of naval mine
attached to a target by magnet
s; they are so named because of their superficial similarity to the limpet
, a type of mollusk
.
A swimmer or diver
may attach the mine, which is usually designed with hollow compartments to give the mine only a slight negative buoyancy
, making it easier to handle underwater.
Usually limpet mines are set off by a time fuze
. They may also have an anti-handling device
, making the mine explode if removed from the hull by enemy divers or by explosions. Sometimes the limpet mine was fitted with a small propeller
which would detonate the mine after the ship had sailed a certain distance, so that it was likely to sink in navigable channel
s or deep water out of reach of easy salvage
and making it harder to determine the cause of the sinking.
(1899-1963) as director of the technical section and under his leadership the team would go on to develop a wide range of innovative weapons.
One of Jefferis' earliest ideas was for a type of mine that could be towed behind a rowboat, but which would attach itself to the hull of a ship that it passed. Getting a heavy bomb to stick to a ship reliably was a problem; the obvious answer was to use magnet
s which should be as powerful as possible.
In July 1939, Jefferis read an issue of the popular magazine Armchair Science
, which contained a small article on magnets:
On 17 July 1939, he contacted the editor of the magazine for more information about the magnets; the editor was Stuart Macrae
.
During the First World War, Macrae had briefly worked on a device for dropping hand grenades from aircraft and he longed for a return to working on such challenges. When Jefferis' call came, he grabbed at the opportunity; he promptly undertook to perform experiments and to produce prototypes. Macrae contacted Cecil Vandepeer Clarke (1897-) then managing director of the Low Loading Trailer Company – Macrae had been editor of a caravan and trailer magazine; he had been impressed by Clarke's work on caravans a couple of years previously and he needed his expertise and the use of his workshops. Macrae and Clarke soon agreed to cooperate on the design of a new weapon, but they quickly abandoned any thought of a towed mine as impractical; instead they worked on a bomb that could be carried by a diver and attached directly to a ship. The new weapon would become known as a limpet mine.
The first versions were put together in a matter of weeks; the innovative design included a ring of small strong magnets for adhesion and the detonator used slowly dissolving aniseed ball
sweets to provide the necessary time to get away.
Just before war was declared, Macrae's name was put forward to Holland who arranged to meet him. Holland considered that Macrae would make a good second in command for Jefferis – he saw Macrae as a capable administrator who could keep his geniuses in order. Macrae joined the War Office as a civilian and Holland saw to it that Macrae got a commission in October 1939 (backdated to 1 September).
Clarke joined the top secret Cultivator No. 6
project as a civilian and later joined the army. He served in the Special Operations Executive
(SOE) with Colin Gubbins
and would later be appointed Commandant of one of the Secret Intelligence Service’s schools. He eventually rejoined Macrae when he was transferred to MD1
in 1942.
The "rigid limpets" used by the British during the Second World War
contained only 4 kilograms (8.8 lb) of explosive, but placed 2 metres (6.6 ft) below the water line they caused a 1 metres (3.3 ft) wide hole in an unarmoured ship.
A smaller version "Clam" was developed from the British limpet for use on land, against which the German innovation known as Zimmerit
was meant to discourage.
, a special operation undertaken in World War II
. In September 1943, 14 Allied
commando
s from the Z Special Unit
raided Japanese
shipping in Singapore
Harbour, sinking seven ships. They paddled into the harbour and placed limpet mines on several Japanese ships before returning to their hiding spot. In the resulting explosions, the limpet mines sank or seriously damaged seven Japanese ships, comprising over 39,000 tons between them.
An example of the use of limpet mines by British special forces was in Operation Frankton
which had the objective of disabling and sinking merchant shipping moored at Bordeaux
, France
in 1942. The operation was the subject of the film The Cockleshell Heroes
.
Limpet mines were also used by the Norwegian Independent Company 1
in 1944 to sink the SS Monte Rosa. On January 16, 1945, 10 limpet mines were placed along the port side of the SS Donau
approximately 50 centimetres (19.7 in) beneath the waterline. These bombs were to detonate once the Donau cleared Oslofjord
and reached open sea, however, the departure time was delayed and the explosion occurred before the Donau reached Drøbak
.
In 1980 a limpet mine was used to sink the Sierra, a whaling vessel which docked in Portugal after a confrontation with the Sea Shepherd. Later that year, about half the legal Spanish whaling fleet was sunk in a similar fashion.
Another notorious use was the sinking of
Greenpeace's Rainbow Warrior
by French DGSE agents in Auckland
harbour, New Zealand
, on July 10, 1985.
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...
attached to a target by magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s; they are so named because of their superficial similarity to the limpet
Limpet
Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...
, a type of mollusk
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
.
A swimmer or diver
Underwater diving
Underwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
may attach the mine, which is usually designed with hollow compartments to give the mine only a slight negative buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
, making it easier to handle underwater.
Usually limpet mines are set off by a time fuze
Fuze
Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...
. They may also have an anti-handling device
Anti-handling device
An anti-handling device is an attachment to or integral part of a landmine or other munition e.g. some fuze types found in air-dropped bombs such as the M83, cluster bombs and sea mines. It is specifically designed to prevent tampering. When the protected device is disturbed it detonates, killing...
, making the mine explode if removed from the hull by enemy divers or by explosions. Sometimes the limpet mine was fitted with a small propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
which would detonate the mine after the ship had sailed a certain distance, so that it was likely to sink in navigable channel
Channel (geography)
In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water...
s or deep water out of reach of easy salvage
Marine salvage
Marine salvage is the process of rescuing a ship, its cargo, or other property from peril. Salvage encompasses rescue towing, refloating a sunken or grounded vessel, or patching or repairing a ship...
and making it harder to determine the cause of the sinking.
History
In December 1938, a new unit was created in the British military that soon became known as Military Intelligence (Research) – usually abbreviated as MI(R) or occasionally as MIR. MI(R) absorbed a technical section that was at first known as MI(R)c. In April 1939, Joe Holland, the head of MIR, recruited his old friend Major Millis Rowland JefferisMillis Jefferis
Major-General Sir Millis Rowland Jefferis KBE MC was, during the Second World War, the founder of a special unit of the British Ministry of Supply which developed unusual weapons.-Early career:...
(1899-1963) as director of the technical section and under his leadership the team would go on to develop a wide range of innovative weapons.
One of Jefferis' earliest ideas was for a type of mine that could be towed behind a rowboat, but which would attach itself to the hull of a ship that it passed. Getting a heavy bomb to stick to a ship reliably was a problem; the obvious answer was to use magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s which should be as powerful as possible.
In July 1939, Jefferis read an issue of the popular magazine Armchair Science
Armchair Science
"Armchair Science" was a British monthly journal of topical and popular science articles published from 1929 to 1940; it ceased publication because of wartime paper shortages. The first editor was A. Percy Bradley, a mechanical engineer associated with Brooklands, then Professor A. M. Low...
, which contained a small article on magnets:
World’s Most Powerful Magnet
- The most powerful permanent magnet in the world – for its size – has been developed in the research laboratories of the General Electric Company in New York.
Only half the size of the eraser on a lead pencil, it will lift a flat-iron weighing 5lb. Its magnetic attraction is several times as strong as that of any previous magnet. The strongly magnetic alloy forming the magnet can be used, too, in electrical equipment to replace electro-magnets that require current.
On 17 July 1939, he contacted the editor of the magazine for more information about the magnets; the editor was Stuart Macrae
Stuart Macrae (inventor)
Colonel Robert Stuart Macrae TD was an inventor best known for his work at MD1 during the Second World War, his best known invention being the sticky bomb.Macrae was the author of Winston Chuchill's Toyshop...
.
During the First World War, Macrae had briefly worked on a device for dropping hand grenades from aircraft and he longed for a return to working on such challenges. When Jefferis' call came, he grabbed at the opportunity; he promptly undertook to perform experiments and to produce prototypes. Macrae contacted Cecil Vandepeer Clarke (1897-) then managing director of the Low Loading Trailer Company – Macrae had been editor of a caravan and trailer magazine; he had been impressed by Clarke's work on caravans a couple of years previously and he needed his expertise and the use of his workshops. Macrae and Clarke soon agreed to cooperate on the design of a new weapon, but they quickly abandoned any thought of a towed mine as impractical; instead they worked on a bomb that could be carried by a diver and attached directly to a ship. The new weapon would become known as a limpet mine.
The first versions were put together in a matter of weeks; the innovative design included a ring of small strong magnets for adhesion and the detonator used slowly dissolving aniseed ball
Aniseed ball
Aniseed balls are a type of hard round sweet sold in the UK, New Zealand and Australia. They are shiny and dark brownish red, and hard like Gobstoppers, but generally only 1cm across. They are generally sold by weight- traditionally, for example, they were sold by quarter pound...
sweets to provide the necessary time to get away.
Just before war was declared, Macrae's name was put forward to Holland who arranged to meet him. Holland considered that Macrae would make a good second in command for Jefferis – he saw Macrae as a capable administrator who could keep his geniuses in order. Macrae joined the War Office as a civilian and Holland saw to it that Macrae got a commission in October 1939 (backdated to 1 September).
Clarke joined the top secret Cultivator No. 6
Cultivator No. 6
Cultivator No. 6 was the code name of a military trench-digging machine developed by the British Royal Navy at the beginning of World War II. The machine was originally known as White Rabbit Number Six; this code name was never officially recognised, but it was said to be derived from Churchill’s...
project as a civilian and later joined the army. He served in the Special Operations Executive
Special Operations Executive
The Special Operations Executive was a World War II organisation of the United Kingdom. It was officially formed by Prime Minister Winston Churchill and Minister of Economic Warfare Hugh Dalton on 22 July 1940, to conduct guerrilla warfare against the Axis powers and to instruct and aid local...
(SOE) with Colin Gubbins
Colin Gubbins
Major-General Sir Colin McVean Gubbins KCMG, DSO, MC was the prime mover of the Special Operations Executive in the Second World War....
and would later be appointed Commandant of one of the Secret Intelligence Service’s schools. He eventually rejoined Macrae when he was transferred to MD1
MD1
Ministry of Defence 1 , also known as "Churchill's Toyshop" was a British weapon research and development organisation of the Second World War....
in 1942.
The "rigid limpets" used by the British during the Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
contained only 4 kilograms (8.8 lb) of explosive, but placed 2 metres (6.6 ft) below the water line they caused a 1 metres (3.3 ft) wide hole in an unarmoured ship.
A smaller version "Clam" was developed from the British limpet for use on land, against which the German innovation known as Zimmerit
Zimmerit
Zimmerit was a coating produced for German armored fighting vehicles during World War II for the purpose of combating magnetically attached anti-tank mines, although Germany was the only country to use magnetic mines against tanks in large scale numbers...
was meant to discourage.
Examples of use
One of the most dramatic examples of their use was during Operation JaywickOperation Jaywick
Operation Jaywick was a special operation undertaken in World War II. In September 1943, 14 commandos and sailors from the Z Special Unit raided Japanese shipping in Singapore Harbour, sinking seven ships.- Background :...
, a special operation undertaken in World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. In September 1943, 14 Allied
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
commando
Commando
In English, the term commando means a specific kind of individual soldier or military unit. In contemporary usage, commando usually means elite light infantry and/or special operations forces units, specializing in amphibious landings, parachuting, rappelling and similar techniques, to conduct and...
s from the Z Special Unit
Z Special Unit
Z Special Unit was a joint Allied special forces unit formed during the Second World War to operate behind Japanese lines in South East Asia...
raided Japanese
Empire of Japan
The Empire of Japan is the name of the state of Japan that existed from the Meiji Restoration on 3 January 1868 to the enactment of the post-World War II Constitution of...
shipping in Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
Harbour, sinking seven ships. They paddled into the harbour and placed limpet mines on several Japanese ships before returning to their hiding spot. In the resulting explosions, the limpet mines sank or seriously damaged seven Japanese ships, comprising over 39,000 tons between them.
An example of the use of limpet mines by British special forces was in Operation Frankton
Operation Frankton
Operation Frankton was a commando raid on shipping in the German occupied French port of Bordeaux in the Bay of Biscay during the Second World War. The raid was carried out by a small unit of Royal Marines known as the Royal Marines Boom Patrol Detachment , part of Combined Operations.The plan was...
which had the objective of disabling and sinking merchant shipping moored at Bordeaux
Bordeaux
Bordeaux is a port city on the Garonne River in the Gironde department in southwestern France.The Bordeaux-Arcachon-Libourne metropolitan area, has a population of 1,010,000 and constitutes the sixth-largest urban area in France. It is the capital of the Aquitaine region, as well as the prefecture...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
in 1942. The operation was the subject of the film The Cockleshell Heroes
The Cockleshell Heroes
The Cockleshell Heroes is a 1955 film with Trevor Howard, Anthony Newley, David Lodge and José Ferrer, who also directed. Set during the Second World War, it is a fictionalised account of Operation Frankton, the December 1942 raid by canoe-borne British commandos on shipping in Bordeaux Harbour...
.
Limpet mines were also used by the Norwegian Independent Company 1
Norwegian Independent Company 1
Norwegian Independent Company 1 was a British SOE group formed in March 1941 originally for the purpose of performing commando raids during the Occupation of Norway by Nazi Germany. It was organized under the leadership of Captain Martin Linge...
in 1944 to sink the SS Monte Rosa. On January 16, 1945, 10 limpet mines were placed along the port side of the SS Donau
SS Donau
SS Donau was a Norddeutscher Lloyd refrigerated cargo ship. In the Second World War the Kriegsmarine used it as a transport ship between Germany and Norway. She became known as the "slave ship" after the SS and Gestapo transported 540 Jews from Norway to Stettin, from where they were taken by...
approximately 50 centimetres (19.7 in) beneath the waterline. These bombs were to detonate once the Donau cleared Oslofjord
Oslofjord
The Oslofjord is a bay in the south-east of Norway, stretching from an imaginary line between the Torbjørnskjær and Færder lighthouses and down to Langesund in the south to Oslo in the north....
and reached open sea, however, the departure time was delayed and the explosion occurred before the Donau reached Drøbak
Drøbak
Drøbak is an unincorporated city and the centre of the municipality of Frogn, in Akershus county, Norway. The city is located along the Oslofjord, and has 13,358 inhabitants....
.
In 1980 a limpet mine was used to sink the Sierra, a whaling vessel which docked in Portugal after a confrontation with the Sea Shepherd. Later that year, about half the legal Spanish whaling fleet was sunk in a similar fashion.
Another notorious use was the sinking of
Sinking of the Rainbow Warrior
The sinking of the Rainbow Warrior, codenamed Opération Satanique, was an operation by the "action" branch of the French foreign intelligence services, the Direction Générale de la Sécurité Extérieure , carried out on July 10, 1985...
Greenpeace's Rainbow Warrior
Rainbow Warrior (1978)
The Rainbow Warrior was a former UK Ministry of Agriculture, Fisheries and Food trawler later purchased by the environmental organisation Greenpeace...
by French DGSE agents in Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...
harbour, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, on July 10, 1985.