According to USNI News, it was confirmed by a US Navy official on Friday that China had the People's Liberation Army Navy send a Type 815 spy ship to an exclusive economic zone off the coast of Hawaii to keep tabs on the biennial exercises.
"We expect the ship will remain outside the territorial seas of the US and not operate in a manner that disrupts ongoing RIMPAC exercise," Capt. Charlie Brown, the spokesperson for the US Pacific Fleet, told the news service. "We've taken all precautions necessary to protect our critical information."
"The ship's presence has not affected the conduct of the exercise," he stressed.
The Dongdiao-class surveillance ship is reportedly the same type of ship that China used surveil previous RIMPAC exercises in 2014 and 2016, USNI reported.
Xu Guangyu, a retired major general who works for the China Arms Control and Disarmament Association, told the South China Morning Post that the vessel was likely sent as a response to the US' surveillance of Chinese ships.
However, the official suggested that ship might just pick up some information about the communication frequencies being used. "While it's operating off Hawaii, the Chinese surveillance ship could acquire some information about the communication frequencies or channels being used during the Rimpac exercise," he told the outlet.
Although China was initially invited to participate in the 2018 games by the US, it was ultimately disinvited in late May for its "continued militarization" of the South China Sea.
"China's continued militarization of disputed features in the South China Sea only serve to raise tensions and destabilize the region," Pentagon spokesman Lt. Col. Chris Logan said in a May statement. "We have disinvited the PLA Navy from the 2018 Rim of the Pacific Exercise. China's behavior is inconsistent with the principles and purposes of the RIMPAC exercise."
"While China has maintained that the construction of the islands is to ensure safety at sea, navigation assistance, search and rescue, fisheries protection, and other non-military functions, the placement of these weapon systems is only for military use," Logan added.
China was first invited to participate in the exercises in 2013, according to The Diplomat. It has only participated twice, once in 2014 and then in 2016.
RIMPAC exercises, which first began in 1971, runs from June 27 to August 2. This year, 25 countries brought a sum of 46 surface vessels, 200 aircrafts and five submarines.