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 long and 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 of C-3 explosive (the forerunner of C-4 explosive) in front of which was laid an array of steel cubes. In total the mine weighed about , and could be fitted with an optional peep sight for aiming. 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 . MacLeod applied for a patent for the mine on 18 January 1956 and was granted it in February 1961. 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. Throner, Kennedy, Bledsoe, and Kincheloe at Aerojet 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