Falcon 9 booster lands after NROL 76 launch. Photo: SpaceX.

SpaceX successfully completed its NROL-76 mission Monday morning, launching a classified satellite from Launch Complex 39A for the National Reconnaissance Office (NRO) before landing the first stage booster on a launch pad nearby.

NROL-76 was originally scheduled to launch on Sunday, but was delayed due to an issue with a sensor on the first stage engine, according to SpaceX.

This launch marks SpaceX’s first for the Department of Defense (DOD) after the U.S. Air Force certified the Falcon 9 to launch satellites for national security purposes in 2015.

Two years ago, SpaceX sued the U.S. Air Force after it awarded an exclusive sole-source launch contract with United Launch Alliance (ULA). The company later dropped the suit, as U.S. Air Force agreed to “[expand] the number of competitive opportunities for launch services.”

SpaceX has won two additional contracts from the U.S. Air Force to orbit satellites for its Global Positioning Satellite (GPS 3) program in 2018 and 2019.

Due to the classified nature of the NROL-76 launch, SpaceX has not released details regarding the satellite’s orbital slot or its specific purpose.