In May, it was announced that the United States was “disinviting” China from participating in the annual Rim of Pacific (RIMPAC) training exercise that aims to increase interoperability between allies national Navies in the Pacific. At the time, the U.S. cited China’s aggressive behavior in the South China Sea, rapidly expanding their military presence and making declarations of sovereignty over international waters that American officials characterized as “running counter to international norms.” Lt. Col. Christopher Logan, a Defense Department spokesperson, said at the time,

The United States is committed to a free and open Indo-Pacific. China’s continued militarization of disputed features in the South China Sea only serve to raise tensions and destabilize the region. As an initial response to China’s continued militarization of the South China Sea we have disinvited the PLA Navy from the 2018 Rim of the Pacific (RIMPAC) Exercise. China’s behavior is inconsistent with the principles and purposes of the RIMPAC exercise.”

The announcement came as little surprise — although China has participated in elements of the RIMPAC exercises of the past, China’s efforts to lay claim to what is perhaps the most heavily traversed waterway on the globe has been the root of rising tensions between the two nations for some time. Despite China’s invitation being revoked, this year’s RIMPAC wasn’t hurting for participants, with 46 vessels hailing from 25 nations participating, along with more than 200 aircraft, five submarines, and an estimated 25,000 people. However, on Friday, the U.S. Navy confirmed that at least one ship from the Chinese People’s Liberation Army-Navy (PLAN) found its way to the drills — an auxiliary general intelligence (AGI) ship that likely belongs to their Dongdiao-class of spy ships.

“It is very disappointing that the presence of a non-participating ship could disrupt the exercise,” Chilean Navy Commodore Pablo Niemann said to journalists regarding China’s decision to send a ship to monitor the RIMPAC exercises. “I hope and expect all seafarers to act professionally so we may continue to focus on the work at hand and building on the spirit of cooperation that gives purpose to this exercise.”