The US Navy held a drill in the Philippine Sea over the weekend.

Two U.S carriers and two amphibious ships, along with their escorts and 26 F-35 Lightning II Joint Strike Fighters drilled with a Japanese large deck warship last week in the Philippine Sea…

“Nothing reaffirms our commitment to a free and open Indo Pacific like [two] Carrier Strike Groups, [two] Amphibious Ready Groups sailing alongside our close friends from the Japan Maritime Self Defense Force,” said Vice Adm. Karl Thomas, Commander, U.S. 7th Fleet in a Facebook post.

It was a dramatic show of force as these photos indicate.

#NavyPartnerships supporting a #FreeandOpenIndoPacific 🇺🇸 ⚓ 🇯🇵 pic.twitter.com/5rppzaGDql

— U.S. Navy (@USNavy) January 23, 2022

The emphasis on a free and open Indo Pacific was definitely a message aimed at China which has been trying to claim territory in the South China Sea as its own. China responded Sunday by sending 39 warplanes toward Taiwan, the largest number so far this year.

Sunday’s incursions were made by 24 J-16 fighter jets, 10 J-10 fighter jets, two Y-9 transport aircraft, two Y-8 anti-submarine warning aircraft, and one nuclear-capable H-6 bomber, the Taiwanese Defense Ministry said in a statement on Sunday.

In response, the Taiwanese military issued radio warnings and deployed air defense missile systems to monitor the activities, it added.

The incursions on Sunday marked the highest daily number of Chinese warplanes entering Taiwan’s ADIZ this year. The highest number of incursions ever recorded was on October 4 last year, when 56 military planes flew into the area on the same day…

Carl Schuster, a former director of operations at the US Pacific Command’s Joint Intelligence Center, said China is trying to keep Taiwan off balance and tired — “like a tennis player pushes his opponent to chase the ball across the court” — sending larger formations of aircraft toward the island from more distant bases on the mainland.

Part of the reason for the naval exercise with Japan may not have been just to send a message about Taiwan but also about the Senkaku Islands, a group of uninhabited islands that lie northeast of Taiwan and about midway between China and Japan. The islands have been controlled by Japan since 1895 (though the US took control of them briefly after WWII). No one has lived on them since a Japanese fish processing plant on one of them closed in the 1940s but the Chinese coast guard routinely approaches them and is chased off by the Japanese coast guard. Just a month ago, the defense ministers for China and Japan held talks about the islands.

During the virtual talks between Japanese Defense Minister Nobuo Kishi and his Chinese counterpart, Gen. Wei Fenghe, the former aired Tokyo’s “grave concerns” about China’s military and coast guard activities, according to Japan’s Defense Ministry readout…

Japan has observed increasingly frequent China coast guard (CCG) activity around the Senkakus since it “nationalized” the islets in 2012. However, the frequency and duration of CCG patrols escalated further after Beijing passed a controversial coast guard law this past February, permitting its armed “white hull” vessels to fire upon foreign ships.

Taiwan remains the big prize in China’s ongoing efforts to expand its control south, but it likely has its eyes on the Senkaku Islands as well. And that matters to the US because an attack on the islands would trigger as US response under the U.S.-Japan Security Treaty, a mutual defense treaty that has been in place since 1960.