Aerojet Rocketdyne AR1a rocket engine has been funded by the U.S. Air Force and does not have customers yet. In 2016, Aerojet received a contract of $350 million from Air Force for the development, testing, and certification of the AR1. In the recent 2021 defense bill, Congress allocated $15 million for the testing of large kerosene engines at Stennis.

The 500,000-pound thrust AR1 is the first oxygen-rich staged combustion kerosene engine of this class built in the United States. The company signed last year an agreement with Firefly Aerospace for the possible use of the AR1 engine, and is in the process of being acquired by Lockheed Martin.