Russia’s out and China is in.

Two years ago it was the other way around.

This year’s Rim of the Pacific war games in and around Hawaii, from late June to early August, are expected to be among the biggest ever, with 23 nations and 25,000 people, officials said.

Russia, a first-time participant during the last RIMPAC with a destroyer, tanker and salvage tug, was invited again but bowed out before the Ukraine crisis erupted, the U.S. Navy’s Third Fleet said.

For its RIMPAC debut, China is expected to send its hospital ship Peace Ark, a destroyer and frigate, according to a Defense Department official.

In 2012, it was China that wasn’t coming — but at that time it wasn’t invited.

The United States was still determining then how it could accommodate the rising Asian power, and future military competitor, in the world’s largest international maritime exercise.

Exactly how much China will participate in the upcoming RIMPAC still hasn’t been detailed by the U.S. Navy, but the People’s Republic is expected to be part of humanitarian assistance and disaster relief exercises, a "group sail," and a photo exercise at the very least.

"Details are still being finalized," Lt. Lenaya Rotklein, a spokeswoman for the Navy’s Third Fleet in San Diego, which helps plan RIMPAC, said Tuesday of the big biennial exercise.

A final RIMPAC planning meeting was held by participating nations, including China, from April 7 to Thursday in San Diego. The final roster of participants, including what they are sending, is expected to be announced early next month, officials said.

The exercise tests the ability of regional navies to work together at sea, and the capabilities of allies to hunt submarines, fire at targets, sink old ships, defend against attack and help in the event of a disaster.

Adm. Harry B. Harris, who commands U.S. Pacific Fleet, said in February that China’s upcoming participation in RIMPAC is an important milestone.

Harris prefaced that by noting the challenges that have come with China’s rise.

"I also have concerns regarding the aggressive growth of the Chinese military, their lack of transparency, and a pattern of increasingly assertive behavior in the East China Sea and South China Sea," the four-star admiral said in prepared remarks for the West 2014 military conference in San Diego.

That behavior has come despite the objections of neighbors, Harris said, adding that attempts to change the status quo negatively affects regional stability.

Despite those concerns, Harris said the United States welcomes the emergence of a prosperous China "as a positive contributor" to Asian stability.

It’s in the best interests of the United States and China to manage friction and prevent misunderstandings at sea, and "that’s what RIMPAC is all about — working with all participating nations in a multilateral way," Harris said.

China’s Peace Ark is described as being "state of the art." Xinhua, the state news agency of China, said the hospital ship, with 300 beds and eight operating rooms, concluded a 16-day medical aid mission in the Philippines in December as it helped with Typhoon Haiyan relief.

Ralph Cossa, president of the Pacific Forum Center for Strategic and International Studies in Honolulu, said sending the Peace Ark to Hawaii for RIMPAC has practical and strategic value.

"It’s a capability that has a great deal of relevance in the HA/DR (humanitarian assistance and disaster relief) field, and I’m sure they (China) want to remind people of that capability — sort of show it off. It’s one of their showcase ships," Cossa said.

It could be China wants to cooperate more with the United States on HA/DR under a new type of power-sharing relationship between the two nations, Cossa said.

At the same time, China can gain practical knowledge, he said.

"It also would give them a little bit of training on how to actually deploy it (the Peace Ark) and use it since they haven’t had a lot of experience in actually sending it out to disaster areas," Cossa said.

Australian media reported that China asked to operate under Australian command during RIMPAC, which would put a layer of government between it and U.S. military control.

A U.S. official said the United States was in agreement with the approach all along.

"The Chinese haven’t had a lot of experience in being part of a multilateral exercise, so this (the Australian involvement) may sort of ease the pain," Cossa said. "But at the end of the day, the overall command of RIMPAC is still an American."

Two years ago, RIMPAC drew 22 nations, 25,000 personnel, more than 40 ships and submarines, and more than 200 aircraft that operated in and around the Hawaiian Islands.

Why Russia backed out last year from the upcoming RIMPAC is unclear. One U.S. defense official said it was because Russian ships were expected to have commitments elsewhere.

The Pentagon announced in early March that it was putting on hold all military-to-military engagements with Russia as a result of its actions in Ukraine.

On Saturday in the Black Sea, the destroyer USS Donald Cook was repeatedly passed at low altitude by a Russian Su-24 Fencer attack aircraft in what the Pentagon called "provocative and unprofessional" Russian actions.