Interdiction Surveillance Center (ISC)
By October 1967, the ISC was ready to receive signals from sensors placed along the Ho Chi Minh Trail by OP-2E Neptunes of VO-67. The Neptunes were replaced by F-4s after three of the OP-2Es were lost on their dangerous missions in Jan-Feb 68. CH-3s of the 21st SOS also dropped sensors along the Trail and in the defense of Khe Sanh.
