 MTDS remained the backbone of Marine Corps air defense operations until it was replaced by the AN/TYQ-23 Tactical Air Operations Module in the early 1990s.The Marine Corps’ air warning program was developed during World War II to provide early warning and fighter control for Marine Corps forces ashore during amphibious operations.Through the 1950s Marine Corps air defense equipment and tactics continued to rely on manual plotting of air tracks based on voice calls from ground control intercept (GCI) controllers.