Editing Claymore mine (section)

=== Throner, Kennedy, Bledsoe, and Kincheloe at Aerojet ===
[[File:M18 claymore US army drawing.svg|right|thumb|The original M18 Claymore mine. The detonator is inserted into the side.]]
In 1954 [[Picatinny Arsenal]] issued a request for proposals (RFP) to improve the M18 as a more effective weapon. At [[Aerojet]] in the early 1950s, Guy C. Throner had independently come up with a design for a Claymore-like mine. He worked with Don Kennedy and the two men submitted a 30-page proposal in response to Picatinny's RFP. They were awarded a $375,000 development contract to improve the Claymore design. The Picatinny criteria for the weapon were as follows:
* It must weigh less than {{convert|3.5|lb|kg|abbr=off}}
* It must throw enough fragments so that at a range of {{convert|55|yd|m}} it achieves a 100 percent strike rate on a {{convert|1.3|sqft|m2|adj=on}} target (man-sized)
* The fragment area must not be more than {{convert|8|ft|m}} high and no more than 60° wide
* Fragments must have a velocity of {{convert|4000|ft/s|m/s}} providing 58&nbsp;[[foot-pounds]] (79&nbsp;[[joules]]) of [[kinetic energy]] delivered to the target.

The requirement for kinetic energy was based on the fact that 58-foot-pounds is required to deliver a potentially lethal injury.<ref>{{cite web|url=https://sill-www.army.mil/famag/2003/MAR_APR_2003/MAR_APR_2003_PAGES_10_12.pdf |title=Engineering the Nonlethal Artillery Projectile |author=Stephen G. Floroff |url-status=live |archive-url=https://web.archive.org/web/20070127055215/http://sill-www.army.mil/famag/2003/MAR_APR_2003/MAR_APR_2003_PAGES_10_12.pdf |archive-date=January 27, 2007}}</ref> Given the requirements of weight and fragment density, approximately 700 fragments were needed, with the ability to aim the mine with an accuracy of around {{convert|2|ft|m|sigfig=1}} at the center of the target zone. The team at Aerojet were given access to all previous research into directional mines, including the M18 and the Phoenix, as well as German research. Dr. John Bledsoe led the initial project.<ref name="Grupp">{{cite book|title=Claymore mines, Their History and Development|author=Larry Grupp|date=May 1993|publisher=Paladin Press|isbn=0-87364-715-7}}</ref>

The original M18 mine fell far short of Picatinny's requirements. One of the first improvements was to replace the steel cubes with {{convert|7/32|in|mm|adj=on}} hardened 52100 alloy ball bearings. These performed poorly for two reasons. Firstly, the hardened steel balls [[spall]]ed into fragments when hit by the shock of the explosion; the fragments were neither aerodynamic enough nor large enough to perform effectively. Secondly, the blast "leaked" between the balls, reducing their velocity.<ref name="Grupp" />

A second problem was the curvature of the mine. This was determined experimentally by Bledsoe, through a large number of test firings. After Bledsoe left the project to work at the Rheem corporation, William Kincheloe, another engineer, came onto the Claymore project.<ref name="Grupp" />

Kincheloe immediately suggested using softer {{convert|1/8|in|mm|adj=on}} steel "gingle" balls, which were used in the foundry process. They did not spall from the shock of the explosive, but deformed into a useful aerodynamic shape similar to a [[.22 Long Rifle|.22 rimfire]] projectile. Using a homemade [[Gun chronograph|chronograph]], the engineers clocked the balls at {{convert|3775|ft/s|m/s}}. The second change 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 experiments, the engineers settled on Devcon-S steel-filled [[epoxy]] to hold the balls in place. With this change, the velocity improved to {{convert|3995|ft/s|m/s}}.<ref name="Grupp" />

Technical challenges to overcome included developing a case to contain the corrosive C-3 explosive that would be durable enough to withstand months of field handling in wide temperature ranges. Using dyes to test various plastics for leaks, they found a suitable plastic called Durex 1661½, which could be easily molded into a case.<ref name="Grupp" />

[[File:Claymore Recon placement.jpg|thumb|300px|left|A [[United States Marine Corps|US Marine]] places a Claymore mine.]]

By the spring of 1956, Aerojet had a near-final design. It was awarded a pre-production contract for 1,000 M18A1 Claymores, designated T-48E1 during testing. The initial versions of the mine used two pairs of wire legs produced from number 9 (3&nbsp;mm) wire. Later when production was ramped up, the design was changed to flat steel scissor, folding-type legs.<ref name="Grupp" />

Early pre-production mines were triggered using a battery pack, which had been used with the M18. This was found to be undesirable for a number of reasons. Bill Kincheloe came up with the idea of using a "Tiny Tim" toggle generator, of the type used with a number of Navy rockets.<ref name="Grupp" /> Originally an aluminum 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.<ref name="Grupp" />

The sighting for the device was originally intended to be a cheap [[pentaprism]] device, which would allow the user to look down from above and see the sight picture. After locating a suitably low-cost device, the engineers found that fumes from either the C-3 explosive or the cement used to glue the sight to the top of the mine corroded the plastic mirrors, rendering them unusable. They adopted simple peep sights, which were later replaced by a [[knife blade sight]].

Testing concluded that the mine was effective out to approximately {{convert|110|yd}}, being capable of hitting 10% of the attacking force. At {{convert|55|yd}}, this increased to 30%. The development project completed, the Aerojet team sent the project back to Picatinny. The Arsenal bid it out to various component suppliers. In 1960 it was type standardized as the M18A1. It was first used in [[Vietnam]] in the spring or early summer 1966.<ref name="Grupp" />

Minor modifications were made to the mine during its service. A layer of tinfoil was added between the fragmentation matrix and the explosive. This slightly improves the fragment velocity, and protects the steel fragments from the corrosive explosive. A [[Ferrite bead|ferrite choke]] was added to prevent RF signals and lightning from triggering the mine.<ref name="Grupp" />