TAIPEI (Taiwan News) — The Ministry of National Defense (MND) reported tracking six Chinese naval vessels and five military aircraft operating around Taiwan between 6 a.m. on Saturday and 6 a.m. on Sunday.

Four of the five People’s Liberation Army (PLA) aircraft crossed the Taiwan Strait median line, entering the nation’s northern and southwestern air defense identification zone (ADIZ), according to the MND.

In response, Taiwan deployed aircraft, naval ships, and coastal-based missile systems to monitor the PLA’s activity.

So far this month, Taiwan has tracked Chinese military aircraft 37 times and naval ships 27 times. Since September 2020, China has increased its use of gray zone tactics by incrementally increasing the number of military aircraft and naval vessels operating around Taiwan.

Gray zone tactics are defined as “an effort or series of efforts beyond steady-state deterrence and assurance that attempts to achieve one’s security objectives without resort to direct and sizable use of force.”