MANILA, Philippines — Chinese coast guard and militia vessels harassed Philippine ships in back-to-back incidents in Ayungin (Second Thomas) Shoal in the West Philippine Sea in April, according to a US think tank.

The two incidents in the Philippine-occupied atoll, which took place several hours apart, were tracked by the Washington-based Asia Maritime Transparency Initiative (AMTI) of the Center for Strategic and International Studies, a think tank that closely follows developments in the South China Sea using satellite images and transponder system.

“China is creating risks of collision on purpose to coerce the Philippines,” Amti director and Southeast Asia expert Gregory Poling told the Inquirer over the weekend.

A 60-meter research vessel of the Philippines Bureau of Fisheries and Aquatic Resources (BFAR) from mainland Palawan was tailed by China Coast Guard (CCG) 5304 “at extremely close distances” of as close as 100 meters in multiple instances as it approached the shoal last April 21, satellite images and vessels automatic identification system broadcasts suggested in the Amtis report published on Friday.

As the CCG 5304 closely pursued the BFAR vessel, three more Chinese vessels closed in from the north: the CCG 5303 accompanied by two Hainan-based militia vessels, the Qiong Sansha Yu 00401 and 00105.

Chinese militia vessels pose as fishing boats but are usually deployed with the CCG to enforce Chinas territorial claims in the South China Sea, including the West Philippine Sea. The Philippine government had protested Chinese militia incursions on several occasions, while Beijing has denied operating a militia.

The BFAR vessel turned around 23.5 kilometers (12.7 nautical miles) from the shoal as it appeared to be “under pressure.” It retreated 24 kilometers (13 nautical miles) east before heading north toward Philippine-occupied Lawak (Nanshan) Island, tailed by the CCG 5304, the Amti said.

Several hours after the first incident, the Philippine Coast Guards (PCG) Parola-class patrol vessel BRP Cape Engaño (MRRV-4411) was seen heading toward the shoal from the east but was met by CCG 5303 and Qiong Sansha Yu 00105, which shadowed it at distances of approximately a nautical mile.

The three vessels stopped approximately 11 kilometers (6 nautical miles) east of the shoal, but three more militia vessels began steaming up from the south: the Qiong Sansha Yu 00009, 00101 and 00110, the Amti said.

Close encounters

The three militia vessels passed less than a mile to the east of the PCG ship before taking up a position at the north end of the shoal.

Another Chinese militia vessel, Qiong Sansha Yu 00214, was tracked near the shoals entrance as the Chinese coast guard and militia ships surrounded the BRP Cape Engaño.

“The vessels all maintained their positions for several hours before the Cape Engaño turned back eastward, encouraged by the approaching 5303, which tailed it until it left the area heading northwest toward unoccupied Whitsun Reef,” the Amti said.

National Task Force for the West Philippine Sea Chair and National Security Adviser Hermogenes Esperon Jr. and Defense Secretary Delfin Lorenzana did not respond to requests for comment about the incidents.

Ayungin Shoal is a low-tide elevation located 194 kilometers (105 nautical miles) off Palawan and is within the Philippines exclusive economic zone. It is occupied by a small military contingent at the BRP Sierra Madre, a World War II landing ship tank intentionally grounded there by the Philippine Navy in 1999 to serve as a military outpost.

China claims the entire South China Sea, including the West Philippine Sea. The Philippines, China, Brunei, Vietnam, Taiwan, and Malaysia have overlapping maritime claims in these waters.

An international arbitral tribunal ruled in 2016 to invalidate Beijings fictitious claims within its so-called nine-dash line, but Beijing refuses to recognize the ruling.

The new incidents in Ayungin Shoal came five months after the Philippine government protested CCG vessels blocking and blasting of water cannons on Philippine boats on a resupply mission to BRP Sierra Madre.

“The long-term plan for China seems to be to make it so dangerous and costly that the Philippines abandons the Sierra Madre,” Poling told the Inquirer.

Getting worse

The AMTI analysis also included two incidents that had been previously reported in the media: Chinas square off with a Taiwanese research vessel in the northern Philippines in March, which included Filipino scientists on board, and CCGs shadowing of ships on a unilateral oil exploration initiated by a Philippine-based firm in the West Philippine Sea in April.

China clearly succeeded with its aggressive tactics, the Amti said, after it convinced the Philippines to reverse a decision to lift a moratorium on oil and gas exploration in the West Philippine Sea. The Duterte administration suspended unilateral exploration activities in April out of concerns over a possible conflict with China.

Poling said he expected China to behave “exactly the same” when President-elect Ferdinand “Bongbong” Marcos Jr., who is perceived by critics as friendly to Beijing, takes office on June 30.

“It didnt change its behavior under [President Rodrigo] Duterte despite all the fawning… Theyve been getting worse year after year but it isnt because Beijing worries about who is in power in Manila. Its a result of Chinas growing strength and Xis aggressive policies,” he said.

Duterte fostered warmer ties with China during his six-year term by setting aside the 2016 ruling against Beijing, expecting investments and loans from the Asian giant that barely materialized until now, with weeks away from the end of his term.

Marcos Jr., meanwhile, recently said he would uphold the 2016 ruling, saying he would not “allow a single millimeter of our maritime coastal rights to be trampled upon.” His remarks were a turnaround from his statements during the campaign that suggested that he would set aside the ruling.

Poling said the Philippines should continue to deepen its alliance with the United States and invest more in its military modernization program to boost deterrence.

It should also rally support for the 2016 arbitration ruling “to impose diplomatic costs and incentivize Beijing to compromise.”

The Philippines continues to seek stronger partnerships on maritime security with allied countries.

Last week, Armed Forces of the Philippines Gen. Andres Centino signed the “Bantay Dagat” (Guardian of the Sea) maritime security framework with US Indo-Pacific Command (Indopacom) commander Adm. John Aquilino, which illustrated both countries resolve “to improve regional maritime domain awareness and confront maritime challenges together.”

The PCG leadership also met with their Japanese counterparts last week for its first-ever bilateral meeting in Tokyo, which centered on countering piracy, capacity building and training, and maritime security operations.