The third in a series of highly secure U.S. military communications satellites began transmitting in January, according to a March 26 press release from prime contractor Lockheed Martin.

The Advanced Extremely High Frequency (AEHF)-3 satellite, built by Lockheed Martin Space Systems of Sunnyvale, Calif., launched in September. 

The first satellite in the constellation, AEHF-1, was launched in August 2010 but took more than a year to reach its operational orbit due to a propulsion glitch. AEHF-2 joined AEHF-1 in orbit in May 2012.  The first two are in limited system testing with a suite of user terminals. 

The satellites are designed to provide assured and highly secure communications links under all conditions, including a nuclear war. One AEHF satellite provides more capacity than the entire legacy Milstar constellation. 

The satellites are used by Canada and the Netherlands in addition to the United States. The United Kingdom is expected to make a connection to the system later this year, the release said.