Editing Claymore mine (section)

=== Norman MacLeod and Calord Corporation ===
[[File:Macleod Claymore patent.png|right|thumb|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, which used the Misnay–Schardin effect to project a spray of {{convert|0.25|in|mm|adj=on}} steel cubes towards the enemy. The cubes were embedded in {{convert|5|lb|kg}} 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 {{convert|20|to|30|m|ft|order=flip|sigfig=1}}.<ref name="Grupp" />

Around 1952 Norman MacLeod, at his company the Calord Corporation, began working on a small directional mine for use by infantry. It is not clear if the United States [[Picatinny Arsenal]] took the concept from the Canadian weapon and asked Norman MacLeod to develop it, or if he developed the design independently and presented it to them. MacLeod designed a weapon called the T-48; broadly similar to the final M18A1, it lacked a number of the design details that made the M18A1 effective.

Through Picatinny, the United States Army accepted the weapon into service as the M18 Claymore and approximately 10,000 were produced. It was used in small numbers in Vietnam from around 1961. It was not until the improved M18A1 was developed that the Claymore became a widely used weapon.

The M18 was {{convert|9.25|in|mm}} long and {{convert|3.27|in|mm}} high, held in 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 {{convert|12|oz|g}} of [[C-3 (plastic explosive)|C-3 explosive]] (the forerunner of [[C-4 explosive]]) in front of which was laid an array of {{convert|0.25|in|mm|adj=on}} steel cubes. In total the mine weighed about {{convert|2.43|lb|kg}}, and could be fitted with an optional peep sight for aiming.<ref>{{ORDATA mines|1073|M18}}</ref> It lacked the later version's iconic "FRONT TOWARD ENEMY" marking. The mine was planted in the ground, using its three sharp legs, and aimed in the direction of enemy approach; at that point, it was fitted with an electrical blasting cap. The mine was 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"; like the Phoenix it had an effective range of only {{convert|90|ft|m|sigfig=1}}.<ref name="Grupp" />

MacLeod applied for a patent for the mine on 18 January 1956, and was granted it in February 1961.<ref>{{cite web|url=https://patents.google.com/patent/US2972949|title=Patent 2,972,949 ANTI-PERSONNEL FRAGMENTATION WEAPON}}</ref> The patent was later the subject of a civil court case between MacLeod, the Army, and Aerojet, which further developed the Claymore design. MacLeod's case collapsed when photographs of the German Trenchmine prototype were produced as evidence of [[prior art]].<ref name="Grupp" />