TAIPEI (Taiwan News) — The defense ministry detected four Chinese military aircraft and 10 naval vessels around Taiwan between 6 a.m. on Sunday and 6 a.m. on Monday.

All four of the aircraft were reported to have crossed the median line of the Taiwan Strait and entered the nation’s southwestern air defense identification zone, or ADIZ. The scale and ADIZ sector of the incursions mirrored those of the previous day.

In response, Taiwan sent aircraft and naval ships and deployed coastal-based missile systems to monitor Chinese activity.

So far this month, Taiwan has tracked Chinese military aircraft 488 times and ships 218 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.”