Continued claims that the EMDrive is being tested on the X-37B
In November 2016 the International Business Times claimed the U.S. government was testing a version of the EmDrive on the Boeing X-37B and that the Chinese government has made plans to incorporate the EmDrive on its orbital space laboratory Tiangong-2. In 2009 an EmDrive technology transfer contract with Boeing was undertaken via a State Department TAA and a UK export licence, approved by the UK MOD. The appropriate US government agencies including DARPA, USAF and NSSO were aware of the contract. However, prior to flight, the propulsion experiment aboard the X-37B was officially announced as a test of a Hall-effect thruster built by Aerojet Rocketdyne.
The X-37B is a US Airforce mini-shuttle. It is usually used for military and intelligence gathering related missions.
The Emdrive is a super controversial propellentless space drive.
Propellentless drive that could be scaled up to a few newtons would enable constant acceleration for years with a nuclear power source. This would enable space travel at significant fractions of light speed.