1948 Bu-4 November 1, 1948 Bu-5 February 24, 1949 Bu-6 April 21, 1949 first stage failed Bu-8 July 24, 1950 at Cape Canaveral pad 3, stage separation error Bu-7 July 29, 1950 at Cape Canaveral pad 3 Bumper 7's WAC Corporal, the last one ever to fly, achieved Mach 9, the highest speed ever achieved by a projectile in the atmosphere at the time. Outcome and legacy The WAC Corporal found itself in direct competition in its designed role, with the V-2 offering much larger payload capabilities that became available in the General Electric-operated Hermes program in April 1946. It was also in competition with the Aerobee, a direct descendant of the Corporal, which was tested in late 1947 and became fully operational in spring 1948. Another competitor was the Neptune sounding rocket, later known as the Viking. The V-2 could lift to , the Aerobee around to over , and Viking to . All three of these offered better performance than the Corporal's payload. In terms of pounds to altitude per dollar, the Corporal also lost to the competition: Each WAC Corporal B cost , for $320/lb to apogee, while each V-2 reassembled from captured parts cost around $30,000 ($14/lb), and the Aerobee cost $18,500 ($123/lb). While the WAC Corporal was soon replaced in its intended role of sounding rocket, its legacy was long-lasting. Its 38ALDW-1500 engine was the direct predecessor of the Nike Ajax's A21AL-2600 and Aerobee's 45AL-2600, and was developed into the AJ10 series, which includes the AJ10-37 engine on the second stage of the world's first purpose-built satellite launch vehicle, Vanguard. Other AJ10 series members include the AJ10-101, which powered the Able upper stage on a variety of launch vehicles, the AJ10-137 Service Propulsion System on the Apollo spacecraft, and the AJ10-190 that acted as the Space Shuttle Orbital Maneuvering System. WAC Corporals are on display at the National Air and Space Museum and in the White Sands Missile Range Museum. Name The origin of the acronym "WAC" in WAC Corporal has been claimed to stand for multiple different phrases. Some White Sands historians (Kennedy, DeVorkin, Eckles) have claimed it means "Without Attitude Control". In "Bumper 8: 50th Anniversary of the First Launch on Cape Canaveral, Group Oral History," William Pickering attributed it to "Women's Army Corps". The earliest public reports of the WAC designation are a series of Aviation Week articles, which seem to support