The Chinese government claims democratically-ruled Taiwan as part of its territory, but the island says it’s already a functionally independent country whose public has shown no interest in being ruled from Beijing. The U.S. sees a Western-leaning Taipei as vital to its own national security and has remained Taiwan’s strongest international backer for decades.

However, as China’s hard power has grown under the leadership of President Xi Jinping, its People’s Liberation Army has expanded its capabilities and reached further from the mainland, with a view to consolidate the country’s maritime and territorial claims in the East and South China seas, and eventually project its forces into the Pacific Ocean.

One consequence of the PLA’s rapid force modernization under Xi has been an increase in Chinese naval and air force operations around Taiwan, which sits in the center of the so-called first island chain, the string of U.S.-friendly territories that effectively hemmed in Chinese forces during the Cold War—but no more.

Robin Hsu, a former Taiwan navy radar operator, heads a team of part-time enthusiasts who track military movements around the island using open-source software, and listen in on, at times, heated radio exchanges between competing militaries.

At around 1:30 p.m. local time on Monday, Hsu intercepted a PLA broadcast while listening to air traffic airwaves. In the recordings, made available to Newsweek, China’s Type 054A frigate Huanggang—pennant number 577—was heard warning an American aircraft to keep its distance.

“U.S. aircraft, this is Chinese navy warship 577. Keep a safe distance and safe altitude from me,” the PLA radio operator said. The U.S. plane wasn’t identified.

The Huanggang is assigned to the naval forces of the PLA’s Eastern Theater Command, also known as the East Sea Fleet.

Hsu, who publishes his recordings online in a bid to increase transparency, is usually based in the south of Taiwan. It means he and his team sometimes track American aircraft conducting intelligence-gathering operations south of the Taiwan Strait and in the Bashi Channel, the strategic waterway connecting the South China Sea to the Western Pacific.

In a separate recording on Tuesday, Taiwan’s Republic of China Air Force was heard attempting to expel a Chinese aircraft from the island’s air defense identification zone (ADIZ). In the years Hsu has been publishing radio intercepts, PLA incursions into Taiwan’s ADIZ have only become more frequent and alarming.

“This is the Republic of China Air Force,” the Taiwan radio operator said at 7:02 a.m. local time. “Attention, PLA military aircraft southwest of Taiwan, altitude 3,000 meters. You have entered our airspace and are affecting aviation safety. Depart immediately.”

Taiwan’s Defense Ministry later confirmed four PLA aircraft, including two fighter jets, had flown sorties into the southwest corner of the ADIZ on July 12.

The frequency of radio exchanges paints a picture of non-stop military maneuvers around Taiwan, whose government and public are gearing up for what many fear could be a resort to force by Beijing in the coming decades.

Equally busy, however, are the seas around the island. On Monday, Japan’s Defense Ministry said the PLA Navy’s Type 053H3 frigate Huaihua—also part of China’s East Sea Fleet—sailed into the Western Pacific via the 70-mile-wide corridor between Japan’s westernmost inhabited island of Yonaguni and Taiwan on July 7 and then returned the same way on Sunday.

On Wednesday, a U.S. Navy carrier strike group led by USS Ronald Reagan entered the South China Sea for the first time this year, according to a statement by the U.S. Seventh Fleet.

“Our strike group works consistently to stay capable and ready and we continue that focus during operations in the South China Sea to demonstrate our commitment to the region,” Rear Adm. Michael Donnelly, commander of Task Force 70 and Carrier Strike Group 5, was quoted as saying.

“Our presence in the South China Sea demonstrates America’s commitment to a free and open Indo-Pacific. Every sailor onboard contributes to this important and enduring mission as we operate in this region, in accordance with international law to ensure that all nations can do the same,” added Capt. Fred Goldhammer, the Ronald Reagan’s commanding officer.