WASHINGTON — The U.S. Air Force on Jan. 20 launched a classified National Reconnaissance Office (NRO) satellite aboard a United Launch Alliance (ULA) Delta 4 Heavy rocket, according to a Jan. 20 ULA press release.

It was the first Delta 4 Heavy rocket to launch out of Vandenberg Air Force Base, Calif., and the largest rocket to ever launch from the West Coast of the United States, the press release said. The previous four Delta 4 Heavy launches have been conducted at Cape Canaveral Air Force Station, Fla.

Whereas the standard Delta 4 rocket uses a single booster core powered by a Pratt & Whitney Rocketdyne RS-68 engine, the rocket’s heavy variant uses three cores that together create nearly 2 million pounds of thrust.