It said the satellite was launched aboard a Titan 4B rocket from the Cape Canaveral, Florida, Air Force Station and placed in geostationary orbit.
"Milstars act as relay stations in space, serving users on foot, ships, submarines and aircraft by transmitting voice communications, data, imagery and video," the industry magazine Spaceflight Now said in its on-line edition.
"Milstar is the world's most secure, nuclear survivable, space-based communications system," said the magazine.
"It performs processing and network routing in space, eliminating the need for vulnerable land-based relay stations and reducing the chances of communications being intercepted on the ground," it said.
The satellite launched Tuesday "will complete the Milstar satellite constellation which provides near-global coverage for the President, the nation's strategic forces, the Air Force's missile warning assets and our operationally deployed military forces," said the magazine.