Two South Korean destroyers arrived at Pearl Harbor on Tuesday for the Rim of the Pacific war games, while other ships are also heading to Hawaii from around the region for the world’s largest international maritime exercise.

The ROKS Sejong the Great and ROKS Kang Gam Chan are the first warships to arrive ahead of the drills, the Navy said.

How big will RIMPAC be this year? In its 25th iteration since its 1971 inception, RIMPAC 2016 will have participation from 27 nations, 25,000 service members, 45 ships, five submarines and more than 200 aircraft.

Twenty-two nations, 49 surface ships, six submarines, more than 200 aircraft and 25,000 personnel participated in 2014, according to the Navy.

The “interoperability” drills, held every other year, are scheduled to run from June 30 through Aug. 4 mostly in Hawaii waters but also off Southern California. Tens of millions of dollars will flow into Hawaii’s economy — mostly at the start and finish of the exercise — and hotels have been advertising RIMPAC packages for months.

Pentagon spokesman Navy Capt. Jeff Davis told reporters Tuesday that RIMPAC “provides a training exercise opportunity that helps participants foster and sustain cooperative relations that are critical to ensuring the safety of sea lanes and security of the world’s oceans.”

It also includes China, which has been increasingly at odds with the United States and more than a few Asian nations over China’s claim of sovereignty over most of the South China Sea.

Last month two Chinese J-11 fighters intercepted a U.S. Navy EP-3 Aries reconnaissance plane in international airspace over the South China Sea, flying within 50 feet of the American aircraft in an encounter described as “unsafe.”

The accusation made by the United States was “groundless,” Chinese Ministry of National Defense spokesman Senior Col. Yang Yujun responded May 26. “The U.S. spy plane flew close to the airspace of China’s Hainan Island for espionage.”

China’s participation comes amid spirited debate over whether it should have been disinvited from RIMPAC, with Defense Secretary Ash Carter recently saying China’s involvement is an example of “militaries working together for common purpose.”

Increasingly, opposition to China’s actions in the South China Sea, as well as fears over North Korean missile advances, are the glue binding together many other Pacific nations — the United States chief among them.

“Chinese participation in RIMPAC will be in compliance with U.S. legislation and regulations,” Davis also said Tuesday. “The U.S. Navy has operational security safeguards to protect U.S. technology and tactics, techniques and procedures from disclosure.”

The Navy said the Chinese destroyer Xi’an, frigates Hengshui and Gaoyouhui, submarine support ship Changdao and hospital ship Peace Ark will be in Pearl Harbor for RIMPAC. A first for the event will be a submarine rescue exercise.

China will be a part of Combined Task Force (CTF 175), led by the U.S. Coast Guard Cutter Stratton and joined by ships from Indonesia, France and the U.S. Navy, and CTF 171, led by U.S. naval expeditionary forces and joined by units from Canada, Australia, New Zealand, South Korea and Indonesia, the Navy said.

China sent four ships to RIMPAC in 2014 for its inaugural participation — while a fifth vessel, a spy ship, stayed far offshore.

South Korea and Japan, finding common ground over a nuclear North Korea, meanwhile, are coming together with the United States for a first-of-its-kind anti-missile drill on the sidelines of RIMPAC off Hawaii.

The exercise, to be held in late June, will involve Aegis ballistic missile defense warships from all three countries sharing detection and tracking information, the Japan Times reported.

The RIMPAC participating nations “will exercise a wide range of capabilities and demonstrate the inherent flexibility of maritime forces,” the Navy said. Those capabilities range from disaster relief and maritime security operations to sea control and complex war-fighting. The training program includes amphibious operations; gunnery, missile, anti-submarine and air defense exercises; counterpiracy operations; mine clearance operations; and explosive ordnance disposal and diving and salvage.

This year’s exercise includes forces from Australia, Brazil, Brunei, Canada, Chile, Colombia, Denmark, France, Germany, India, Indonesia, Italy, Japan, Malaysia, Mexico, the Netherlands, New Zealand, Norway, China, Peru, South Korea, Philippines, Singapore, Thailand, Tonga, the United Kingdom and the U.S.

This is the first time that Brazil, Denmark, Germany and Italy are participating in RIMPAC.

The centerpiece of the U.S. Navy will be the aircraft carrier John C. Stennis.

The Royal New Zealand Navy will have a key role in command of an amphibious task force of 13 ships from the flagship USS America. The Canadian warships Calgary and Vancouver, meanwhile, left Monday for Hawaii and RIMPAC. Canada said the exercise will allow it to test electronic countermeasures and fire Evolved Seasparrow and Harpoon missiles as well as heavyweight torpedoes.