TAIPEI (Taiwan News) — Four fighter jets and one anti-submarine helicopter from China entered Taiwan’s air defense identification zone (ADIZ) Saturday (April 23), the Ministry of National Defense said.

Apart from four Shenyang J-16 jets, the itinerary of a KA-28 ASW airship showed a Chinese People’s Liberation Army Navy (PLAN) ship must be plying the waters southwest of Taiwan, the Liberty Times reported.

The Russian-made Kamov helicopter is usually based on Navy ships, while no Chinese land bases were available close enough to the area where Taiwan’s military spotted the airship.

The four jets appeared in the southwestern sector of the ADIZ and soon turned back after Taiwan’s military sent aircraft, issued radio warnings, and deployed air defense missile systems to track the planes.