BEIJING — China’s homemade J-20 stealth fighter has conducted sea training for the first time, the Air Force said Wednesday.

The recent mission took the plane or planes out to sea for drills under “actual war conditions,” Air Force spokesman Senior Col. Shen Jinke posted to the service’s microblog. He called that a “further upgrade of the Air Force’s combat capabilities.”

China said in February that the plane had obtained initial operational capability and was being introduced into combat units.

First flown in 2011, the J-20 is China’s answer to fifth-generation jets such as the U.S. F-22 and F-35.

With its stealthy capabilities, speed and maneuverability, it potentially represents a major upgrade to Chinese air power, although questions have been raised about some of its technology, specifically its engines.

Though domestically developed, the J-20 is believed to have initially relied on Russian engines for propulsion due to manufacturing problems in China.

Some reports say they have since been replaced with Chinese engines, the WS-10B, which do not have a big enough thrust-to-weight ratio to allow the J-20 to cruise at supersonic speeds without using afterburners, something that would expose it to detection.

China increased its defense budget by 8.1 percent this year to 1.1 trillion yuan (U.S. $172.7 billion) as it prepares to launch its second aircraft carrier and field an array of advanced warplanes and missiles able to attack air and sea targets at vast distances.