On July 19, 1962, the Nike-Zeus program conducted its seventh mission (ZK-7) at the Kwajalein Missile Range. This was also the first attempt to intercept an intercontinental ballistic missile, or ICBM.The Zeus (Missile 20071) was pitted against an Atlas-D nose cone travelling at 16,000 mph. The Zeus missile came within 2 km of the warhead, close enough that the nuclear warhead of a fully operational Zeus would have destroyed the ICBM warhead.The eight-story Atlas ICBM was launched from Vandenberg Air Force Base, California, by a combat crew from the 565th Strategic Air Command Squadron at Francis E. Warren, Air Force Base, Wyoming.The 48-foot Nike-Zeus was sent "screaming aloft" from Mount Olympus on Kwajalein Island. The intercept occurred "within minutes -- possibly three." This was the first interception of an ICBM ballistic target, flown at true ICBM range, speed and trajectory.The test caught the imagination of the nation as just days earlier Soviet Premier Nikita Khrushchev had announced that the Soviet Union had a missile that could hit a fly in space. A report in the Kwajalein Hourglass newspaper from July 20, noted that now the United States had its own flyswatter.On Kwajalein itself, the test, a culmination of six years of planning, was celebrated as a "spectacular" show, with spontaneous celebrations across the island. In Washington, the House Space Committee Chairman George Miller described the event as evidence of "one of the greatest breakthroughs" in recent defense development. Meanwhile, one contemporary wire service release hailed the test as a "majestic bullseye, comparable some have said, to a bullet hitting a bullet."In the official records, however, this system test was deemed only a partial success. The radars had performed as projected -- acquiring the target, transferring the track from one radar to the next, and guiding the Zeus to its target. Following the launch, the Zeus then came within 2 km, a lethal distance, of the Atlas D. This larger-than-planned miss distance "resulted from the ZEUS missile losing hydraulic power due to excessive roll during the last 10 seconds before intercept."Miss distance is the distance between the target and the defensive missile at the instant of commanded warhead burst. This is the principal measure of performance of an AICBM system. Given its significance, the ABM Project History explained "to avoid suspicion of any self-generated miss distance within the Zeus system considerable effort was directed at finding an independent miss-distance recorder for the Zeus system tests at Kwajalein."The Nike-Zeus Project Office examined two options to calculate the miss distance. Ultimately the Radio Doppler Miss Distance Indicator, which used an adapted Navy AN/US-Q-11 Radio Doppler miss-distance measuring set, was adopted.Developed by the Physical Science Laboratory of the New Mexico State University, the indicator, created originally for the Highball and Speedball test rocket targets being developed for the Zeus tests, was adapted further to support ICBM tests. Tests conducted in December 1961 successfully demonstrated that signals from a UHF radio transmitter mounted in a reentry ICBM nose cone could "penetrate the surrounding plasma sheath."To calculate the miss distance, a transmitter was emplaced in the ICBM and a comparable receiver into the Zeus missile. A reading taken at the time of the burst-command, would determine the miss distance. As described in the Project History, "the resultant shape of the Doppler signal telemetered to ground during intercept, when correlated to the burst-command time, provided an independent measurement of miss distance." The resulting figures correlated "reasonably well" with the Nike-Zeus' self-generated miss-distance numbers.