1958, was the AN/FPS-16, on which NRL and RCA collaborated. The earliest version, XN-1, utilised a metal plate lens. The second version XN-2 used a conventional 3.65 meter [12 ft] parabolic antenna, and was the version which went to production. These radars played an important part in the Mercury, Gemini, and early Apollo missions, being deployed in Bermuda, Tannarive, and Australia, among other places for that purpose. The IRACQ [Increased Range ACQuisition] modification was installed on certain of these installations; certainly the one located at Woomera, Australia was so modified. One of the larger installations first appeared in the 1970s as the US Navy's AN/SPY-1 radar used on the Aegis Combat System, and MK-74 radar used on Tartar Guided Missile Fire Control System and research. The cost and complexity of implementing monopulse tracking was reduced and reliability increased when digital signal processing became available after the 1970s. The technology is found in most modern tracking radars and many types of disposable ordnance like missiles. References See also Amplitude monopulse Phase-comparison monopulse AIRPASS Radar Radar imaging Multidimensional signal processing