Mainor relieved Capt. Chase Sargeant as Destroyer Squadron 15’s commanding officer during a ceremony aboard the guided missile destroyer Benfold, the report said.
The squadron is the main battle arm of the US Navy’s 7th Fleet stationed at Yokosuka Naval Base in Japan.
The warships provide the nuclear-powered aircraft carrier Ronald Reagan with escorts and make freedom-of-navigation patrols around the Taiwan Strait and the South China Sea to show the United States’ resistance to Chinese maritime claims in the area, the report said.
Vice Adm. Karl Thomas, Commander of the 7th Fleet, outlined to Mainor the geopolitical context in which he finds himself serving the US Navy in the Indo-Pacific, the report said.
"I think it’s safe to say that our rules-based international order is now significantly threatened," the report quoted Thomas as saying. "What you [Mainor] do now matters, you can give our president the ability to deter the aggressors and ensure a free and open word - never forget that."
A visit by US House Speaker Nancy Pelosi to Taiwan earlier in August significantly increased tensions between Washington and Beijing, with China conducting naval and air exercises around the island in response to the congressional trip.
Beijing condemned Pelosi’s visit as a violation of China’s national and territorial sovereignty, while the Biden administration defended the trip as being within the boundaries of US-China agreements on Taiwan.
Mainor began his service in the US Navy as an enlisted sonar technician, later working in roles that included commanding the mine countermeasures ship Patriot and the Arleigh Burke-class guided missile destroyer William P. Lawrence, the report said.
Mainor also served as Executive Assistant to the Navy Chief of Legislative Affairs and Deputy Commodore of Destroyer Squadron 15, the report added.