M18A1 Claymore Antipersonnel Mine
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M18A1 Claymore mine
The M18A1 Claymore mine with the plastic trigger and detonator wire.
Type Direction fragmentation anti-personnel mine
Place of origin United States
In service 1960-
Used by United States
Wars Vietnam War
Designer Norman Macleod and others (see article)
Weight 3.5 lbs
Length 216 mm
Width 38 mm
Height 124 mm
Caliber 700 1/8 inch steel balls
Muzzle velocity 3,995 fps (1,200 m/s)
Effective range 50 m
Maximum range 250 m
Sights Peep sight on early models, later a knife edge sight
Filling weight 680 g
mechanism Two detonator well for electrical detonators
The M18A1 Claymore is a directional anti-personnel mine used by the U.S. military. It was named after the large Scottish sword by
its inventor, Norman A. MacLeod. The Claymore fires shrapnel, in the form of steel balls, out to about 100 meters across a 60° arc in
front of the device. It is used primarily in ambushes and as an anti-infiltration device against enemy infantry. It is also of some use
against soft-skinned vehicles.
Numerous licensed and unlicensed copies of the mine are produced in numerous countries. Examples are the former Soviet Union
models MON-50, MON-90, MON-100, MON-200; MRUD (Serbia); No. 6 (Israel); MAPED F1 (France); Mini MS-803 (South Africa), and
2.1 Norman Macleod and Explosive Research Corporation
2.2 Kennedy, Throner, Bledsoe, and Kincheloe at Aerojet
3 Mine ban treaty
4 National copies
5 See also
7 External links
The M18A1 Claymore mine consists of a horizontally convex olive green plastic case (inert training versions are blue), which is
vertically concave. The shape was developed through experimentation to deliver the optimum distribution of fragments at 50 meters
(55 yards) range. The case has the words "Front Toward Enemy" embossed on the front surface of the mine. A simple open sight is
provided for aiming the mine on the top surface. Two pairs of scissor legs attached to the bottom support the mine and allow it to be
aimed vertically. Either side of the sight are fuse wells set at 45 degrees to the vertical. Internally the mine contains a layer of C-4
explosive on top of which is a matrix of approximately seven hundred 1/8 inch diameter steel balls set into a epoxy resin.
When the M18A1 is detonated, the explosion drives the matrix of 700 spherical fragments out of the mine at a velocity of 3,995 feet
per second (1,200 m/s) , at the same time breaking the matrix into individual fragments. The spherical steel balls are projected in
a 60° fan-shaped pattern that is two meters high (6 ft, 8 in) and 50 meters (165 ft) wide at a range of 50 meters (165 ft). The force of
the explosion deforms the relatively soft steel fragments into a shape similar to a .22 rimfire projectile . These fragments are
moderately effective up to a range of 100 meters (328 ft), with a hit probability of around 10% on a man-sized 1.3 square foot target
(0.12 square meters). The fragments can travel up to 250 meters (820 ft) forward of the weapon. The optimum effective range is 50
meters (165 ft), at which the optimal balance is achieved between lethality and area coverage with a hit probability of 30% on a man-
sized target. The weapon and all its accessories are carried in the M7 bandolier. An instruction sheet for the weapon is attached to
the inside cover of the bandolier.
The Claymore mine is typically deployed in one of three modes: Controlled, Uncontrolled, or Time-delayed.
Controlled Mode (also known as Command Detonation)
The mine is detonated by the operator as the forward edge of the enemy approaches a point within the killing zone (20 to 30 meters
(65 to 100 ft)) where maximum casualties can be inflicted. Controlled detonation may be accomplished by use of either an electrical
or nonelectrical firing system. When mines are employed in the controlled role, they are treated the same as individual weapons
and are reported for inclusion in the unit fire plan. They are not reported as mines; however, the emplacing unit must ensure that the
mines are removed, detonated, or turned over to a relieving unit. The M57 Firing Device (colloquially referred to as the "clacker") is
included with the M18A1 Claymore Mine so that it can be used in the controlled mode. When Claymore Mines are daisy chained
together, one M57 firing device can initiate several claymore mines.
Uncontrolled Mode (also known as Victim Initiated Detonation)
Uncontrolled firing is accomplished when the mine is installed in such a manner as to cause an unsuspecting enemy to detonate
the mine. Mines employed in this manner must be reported and recorded as land mines. There are many mechanisms that can be
used to initiate the M18A1 in uncontrolled mode, including the M142 Multipurpose Firing Device, M5 Pressure Release Device
(mousetrap), tripwires, strikers, infrared sensors, acoustic & vibration sensors.
Time-delayed firing involves the fitting of a short timed fuse and a fuse igniter to allow the mine to be used as a pursuit deterrent.
This, anecdotally, may be combined with a CS grenade or bag containing the irritant contained in a CS grenade. The mine is
emplaced, quickly oriented on the direction pursuers are most likely to take, and the fuse is ignited before the position is abandoned.
The development of the M18A1 mine dates back to work done during World War II. The Misznay-Schardin effect was independently
discovered during World War II by Misznay, a Hungarian, and Dr. Hubert Schardin, a German. When a sheet of explosive detonates
in contact with a heavy backing surface (for example, a metal plate), the resulting blast is primarily directed away from the surface in
a single direction. Schardin spent some time developing the discovery as a side-attack anti-tank weapon, but development was
incomplete at the end of the war. Schardin also spent time researching a "Trench mine" that used a directional fragmentation effect.
 Norman Macleod and Explosive Research Corporation
Images from the 1956 Macleod patent.Following the massed Chinese attacks during the Korean War, Canada and the United
States began to develop projects to counter them. Canada fielded a weapon called the "Phoenix" landmine that used the Misznay-
Schardin effect to project a spray of 0.25 inch steel towards the enemy. The cubes were embedded in five pounds of Composition B
explosive. It was too large to be a practical infantry weapon and was relatively ineffective with a maximum effective range of only 20 to
30 yards (20 to 30 meters). 
Around 1952 Norman Macleod at his company the Explosive Research Corporation began working on the concept of a small
directional mine for use by infantry. It is not clear if Picatinny took the concept from this Canadian weapon and asked Norman
Macleod to develop it; or if he came up with the idea independently and presented it to them. Macleod came up a design, the T-48
that was broadly similar to the final M18A1, although it lacked a number of the design details that made the M18A1 effective. It was
accepted into Army service as the M18 Claymore and approximately 10,000 were produced. It was used in small numbers in
Vietnam from around 1961, but it wasn't until the arrival of the improved M18A1 that it became a significant weapon.
The M18 was 235 millimeters long and 83 millimeters high with a plastic case with three folding spike legs on the bottom. An
electrical blasting cap for triggering the mine was inserted through a small hole in the side. Internally the mine consisted of a layer
of 340 grams of C-3 explosive (the forerunner of C-4 explosive) in front of which was laid an array of 0.25 inch steel cubes. In total
the mine weighed about 1.1 kilograms, and could be fitted with an optional peep sight for aiming. . It lacked the later versions
iconic "Front towards enemy" marking. The mine was planted in the ground using its three sharp legs and was aimed in the
direction of enemy approach and then fitted with an electrical blasting cap. The mine was then triggered from a safe position,
preferably to the side and rear.
The mine was barely more than a prototype and was not considered a "reliable casualty producer" with an effective range like the
Phoenix of only 90 feet (30 meters). 
Macleod applied for a patent for the mine on 18 January 1956 and was granted it in February 1961.  The patent was later the
source of a civil court case between Macleod, the Army and Aerojet who proceeded to develop the design further. Macleod's case
collapsed when photographs of the German Trenchmine prototype were produced as evidence of prior art. 
 Kennedy, Throner, Bledsoe, and Kincheloe at Aerojet
The original M18 Claymore mine. Note the detonator inserted into the side.In 1954 Picatinny issued a request for proposals (RFP)
aimed at improving the M18 into a more effective weapon. Guy C. Throner working at Aerojet had independently come up with a
design for a Claymore like mine in the early 1950s. Seeing the RFP and working with Don Kennedy they submitted a 30 page
proposal to Picatinny and were awarded a $375,000 development contract to improve the design. Picatinny criteria for the weapon
were as follows
It must weigh less than 3.5 pounds (1.6 kilograms)
It must throw enough fragments so that at a range of 55 yards (50 meters) it achieves a 100 percent strike rate on a 1.3 square feet
target (man sized)
The fragment area must not be more than 8 feet (2.4 meters) high and no more than 60 degrees wide
Fragments must have a velocity of 4,000 feet per second (1,200 meters per second) providing 58 foot-pounds (79 joules) of kinetic
energy delivered to the target.
The requirement for kinetic energy came from the fact that 58 foot pounds is the amount of kinetic energy required to deliver a
potentially lethal injury . Given the requirements of weight, and fragment density required this dictated using approximately 700
fragments, and being able to aim the mine with an accuracy of around two feet (0.6 meters) at the center of the target zone. The
team at Aerojet were given access to all previous research into the directional mine, including the M18 and the Phoenix mine, as
well as German research. Dr. John Bledsoe led the initial project. 
In testing it became apparent that the original M18 mine fell far short of the Picatinny requirements. One of the first improvements
was to replace the square cubes with 7/32 inch hardened 52100 alloy ball bearings. These performed poorly for two reasons, the
hardened steel balls, spalled into fragments when hit by the shock of the military explosive, the fragments were neither aerodynamic
nor large enough to perform effectively. Additionally the blast "leaked" between the balls, actually reducing the maximum velocity of
A second problem to be addressed was the optimum curvature of the mine. This was determined experimentally by Bledsoe,
through a large number of test firings. Bledsoe left the project to work at the Rheem corporation, and another engineer, William
Kincheloe came onto the project.
Kincheloe immediately came up with the suggestion to use softer 1/8 inch steel "gingle" balls that were used in the foundry
process. The softer balls did not spall when struck by the shock from the explosive, instead they deformed into a useful
aerodynamic shape similar to a .22 rimfire projectile. Using a homemade Chronograph these were clocked at 3,775 feet per
second (1,150 meters per second). The second optimization was to use a poured plastic matrix to briefly contain the blast from the
explosive, so that more of the blast energy was converted into projectile velocity. After a number of weeks of experimentation they
finally settled on Devcon-S steel filled epoxy to hold the steel balls against the explosive. With this in place the velocity improved to
3,995 feet per second (1,200 meters per second).
There were still a number of technical challenges to overcome, including the development of a case that would be able to contain
the corrosive C-3 explosive, and be tough enough to withstand months of field handling in wide temperature ranges. Using soluble
dyes they found a suitable plastic called Durex 1661 1/2 which could be easily molded into a case.
By the Spring of 1956 they had a near final design, which was awarded a preproduction contract for 1,000 M18A1 claymores
designated T-48E1 during testing.
The initial versions of the mine used two pairs of spindly wire legs produced from number 9 wire. Later when production was
ramped up the design was changed to flat steel scissor, folding-type legs.
Early pre-production mines were triggered using a battery pack that was used with the M18, however this was undesirable for a
number of reasons. Bill Kincheloe came up with the idea of using a "Tiny Tim" toggle generator used with a number of Navy
Rockets. Originally an aluminium box was used to hold the generator. Later a Philadelphia company "Molded Plastic Insulation
Company" took over the manufacture of the firing device for the first large scale production run producing a plastic device.
The sighting for the device was also originally intended to be a cheap pentaprism device, that would allow the user to look down
from above and see the sight picture. After finding a suitably low cost device, it was found that fumes from either the C-3 explosive or
the cement used to adhere the sight to the top of the mine corroded the plastic mirrors, rendering it unusable. In the end simple
peep sights were adopted, which was later replaced by a knife blade sight.
Testing conducted with the mine concluded that the mine was effective out to approximately 110 yards, being capable of hitting 10 %
of the attacking force. At 55 yards this increased to 30 %. The development project completed, the Aerojet team sent the project back
to Picatinny, where it was bid out to various component suppliers. And it was standardized at the M18A1 in 1960 seeing first active
service in Vietnam in Spring or Early Summer 1966.
 Mine ban treaty
When in use by the U.S. Military, the M18A1 Claymore Anti-Personnel Mine is most often command-detonated. Such use is
permitted by the Mine Ban Treaty. However, use of Claymore mines in uncontrolled (tripwire) mode is prohibited by the treaty.
Because of this uncontrolled mode, it is frequently listed in efforts to ban anti-personnel mines. While the United States has been
an active participant in worldwide demining operations, and has signed the 1996 Protocol on Prohibitions or Restrictions on the
Use of Mines, it has not signed the 1997 Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-
Personnel Mines and on their Destruction, commonly known as the land mine ban treaty. Under the 1996 Protocol on Prohibitions
or Restrictions on the Use of Mines the US forces may legally use the claymore in victim initiated detonation as long as provisions of
the protocol are met. Provisions of the protocol center around confining landmines to clearly known and marked areas such that the
chances of civilian incursion into mined areas is so low as to minimize civilian risks and casualties. As such, it is a requirement for
individual U.S. soldiers and Marines to know how to properly deploy and emplace the M18A1 landmine in compliance with
 National copies
A number of licensed and unlicensed copies of the mine were produced.
Type 66 China
KM18A1 South Korea
K440 South Korea, slightly smaller than the Claymore with 770 fragments.
No 6 Israel
VS-DAFM 7 Italy 
P5 Mk1 Pakistan
Arms-Tech MM-1 "Minimore" United States, a smaller variant conceived for Special Forces use
Shrapnel mine No 2 South Africa
Försvarsladdning 21 Sweden
FFV-013 Sweden 
LI-12/Truppmina 12 Sweden 
 See also
Military of the United States Portal
List of individual weapons of the U.S. Armed Forces
^ a b c d e f g h i Larry Grupp. Claymore mines, Their History and Development. Paladin Press. ISBN 087364-715-7.
^ M18 at ORDATA
^ Patent 2,972,949 ANTI-PERSONNEL FRAGMENTATION WEAPON.
^ Stephen G. Floroff. Engineering the Nonlethal Artillery Projectile.
^ Banning Antipersonnel Mines. Landmine monitor 2001 report.
^ VS-DAFM 7 Italian anti-personnel "Claymore" mine. Technical specs at James Madison University - Mine Action Informations
^ FFV-013 Swedish anti-personnel "Claymore" mine. Technical specs at James Madison University - Mine Action Informations
^ LI-12/Truppmina-12 Swedish anti-personnel "Claymore" mine. Technical specs at James Madison University - Mine Action
 External links
Wikimedia Commons has media related to:
M18A1 Claymore Antipersonnel MineGlobalSecurity.org - M18 Claymore
International Coalition to Ban Landmines - Countries using Claymore type mines (PDF)
GlobalSecurity.org - FM 23-23 ANTIPERSONNEL MINE M18A1 AND M18 (CLAYMORE) Field Manual
Retrieved from "http://en.wikipedia.org/wiki/M18A1_Claymore_Antipersonnel_Mine"
Category: Antipersonnel mines
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