TAIPEI (Taiwan News) — The defense ministry detected five Chinese military aircraft, six naval vessels, and one official ship around Taiwan between 6 a.m. on Sunday and Monday.

Four out of the five aircraft were reported to have crossed the median line of the Taiwan Strait and entered the nation’s northern air defense identification zone, or ADIZ. In response, Taiwan sent aircraft and naval ships and deployed coastal-based missile systems to monitor the Chinese activity.

In August so far, Taiwan has tracked Chinese military aircraft 41 times and ships 28 times. Since September 2020, Beijing has increased its use of “gray zone tactics” by operating military aircraft and naval vessels around Taiwan.

CSIS defines gray zone tactics 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.”