Warships from 26 countries are arriving in the Hawaiian Islands for the biennial Rim of the Pacific exercise, the world’s largest recurring naval war game.

About 25,000 military personnel will participate in RIMPAC 2022, which kicks off Wednesday and will run through Aug. 4, with 38 surface ships, four submarines and more than 170 aircraft. The exercise, hosted by the Hawaii-based U.S. Pacific Fleet, comes at a time of increased global conflict and diplomatic tensions.

It also comes as relations between Hawaii residents and Navy commanders have been severely strained after jet fuel stored at the Navy’s underground Red Hill fuel storage facility spilled in November into the service’s water system that serves 93,000 Oahu residents.

RIMPAC 2022 is a return to full scale after the COVID-19 pandemic unexpectedly forced major changes to the previous exercise. The Pacific Fleet had hoped RIMPAC 2020 would be the largest iteration of the exercise yet but hastily scaled back as COVID-19 rapidly spread worldwide.

Instead of the usual two months, the exercise was cut to two weeks and only seven countries participated. Amphibious landings as well as shore leave were canceled to ensure the exercise was entirely at sea and that crews and island residents weren’t exposed to one another.

Activists and some local elected officials called for it to be canceled due to fears it would spread the disease. Opponents pointed to an outbreak aboard the aircraft carrier USS Theodore Roosevelt that infected 1,156 crew members and killed one — forcing some of the crew to quarantine in hotels on Guam. The 2020 exercise ultimately went by without incident.

But RIMPAC 2022 also is under scrutiny as the Navy inches toward removing fuel from Red Hill, where 20 massive tanks sit just 100 feet above a critical aquifer that provides much of Oahu’s drinking water. The tanks can store up to 250 million gallons, though are currently believed to be holding closer to 180 million. The Navy has kept the amount secret, citing security concerns.

The fuel reserve in Red Hill previously played a role during RIMPAC as the world’s navies congregated in Hawaii. During RIMPAC 2018, the Red Hill facility provided over 19 million gallons of fuel to participating U.S. and foreign ships and aircraft, according to a Navy news release at the time.

“Questions remain whether there were any Red Hill fuel spills during the 2018 and 2020 RIMPAC fueling as the defects in the pipelines were present then as they are now,” said Melodie Aduja, co-chair of the Democratic Party of Hawaii’s Environmental Caucus.

But officials insist that this year they will make due without Red Hill. At Joint Base Pearl Harbor-Hickam, Pearl Harbor has six above-ground tanks called the Upper Tank Farm that hold 36 million gallons, and Hickam has four above-ground tanks that store about 14 million gallons.

Cmdr. Sean Robertson, the Navy’s spokesperson for the RIMPAC exercise, said participants would be relying on the Upper Tank Farm for fuel and will be doing most refueling at sea. The only in-port refueling during the exercise will be at Pearl Harbor’s Hotel Pier, the main fuel pier for the facility.

“RIMPAC will primarily exercise the at-sea fuel storage and transfer concept using two large fuel tankers which hold approximately 12 million gallons each,” Robertson said. “These tankers will provide fuel to combat logistics force ships, who will then transfer to surface ships at sea. Combat logistics force ships are highly specialized units designed to transfer fuel in an effective and safe manner.”

The Red Hill crisis has made the Navy the subject of criticism and a series of lawsuits in Hawaii. A third-party contractor review commissioned by the Navy found that Red Hill’s pipes are in a state of profound disrepair and that it might take months or years — along with millions of dollars — to make enough repairs to safely drain the tanks without causing further contamination of the island’s water resources.

“The countless hours and millions of taxpayer dollars used to plan and host RIMPAC could have been used to help expedite the defueling of Red Hill,” said Wayne Tanaka, director of the Sierra Club’s Hawaii chapter. “Instead, our island’s ability to support our people — including military personnel and their families — remains at daily risk, with the added threats and strains that come with RIMPAC. It’s like the Navy came to our house, started a kitchen fire, and are now hosting a backyard barbecue while it continues to burn.”

Plans for this year’s exercise are ambitious. Alongside the U.S., the exercise will have participants from Australia, Brunei, Canada, Chile, Colombia, Denmark, Ecuador, France, Germany, India, Indonesia, Israel, Japan, Malaysia, Mexico, the Netherlands, New Zealand, Peru, the Republic of Korea, the Philippines, Singapore, Sri Lanka, Thailand, Tonga and the United Kingdom.

“Environmental stewardship is a top priority for all RIMPAC participants and we are making every effort to ensure we fuel all RIMPAC units in an environmentally conscious manner,” Robertson said.

It will be the first RIMPAC since the U.S., Australia and U.K. signed the AUKUS agreement, a trilateral security pact made public in September that is aimed at tightening cooperation between the three countries on the development and acquisition of nuclear-powered submarines and new missile technology.

It’s also going to be the first RIMPAC for the Kaneohe- based 3rd Marine Littoral Regiment, which activated at Marine Corps Base Hawaii in March. The unit, which is set to provide a blueprint for an eventual reorganization of the entire Marine Corps, is centered on amphibious operations in support of the Navy during island and coastal fighting. The strategy is largely aimed at operations in the Western Pacific, particularly the South China Sea.

The Chinese navy attended RIMPAC in 2014 and 2016 as an invited guest to practice humanitarian and search-and-rescue missions with the U.S. Navy, but was disinvited in 2018 before the exercise began amid souring relations between Washington and Beijing.

Several of China’s neighbors, including RIMPAC participants, have been embroiled in territorial disputes with China. Beijing considers almost the entire South China Sea to be its exclusive territory within a maritime border called the “Nine-Dash Line.” The Philippines issued a legal challenge, and in 2016 an international court ruled that most of Beijing’s claims had no legal basis.

But the Chinese military has dug in, stationing troops and building bases on disputed land formations, and sometimes attacking vessels from neighboring countries. The standoff has increasingly militarized a critical waterway through which at least a third of all global trade travels.

While China is the main concern of U.S. commanders in the Pacific, Russia is still a player in the region. Last year Russia’s navy held what Russian officials said was its largest Pacific exercise since the end of the Cold War just west of Hawaii, prompting Hawaii Air National Guard fighters to scramble several times but without confrontations.

Since Russian forces pushed into eastern Ukraine in February — turning what was a grinding low-intensity conflict into a full-scale conventional war — tensions have sharply escalated. The Kremlin has found itself increasingly isolated from the international community as it deals with sanctions and boycotts. Before the latest invasion, Russia was one of Hawaii’s top sources of oil.

But Russia continues to have a strong trading relationship with China, and the two countries have seemingly stepped up military cooperation. Last week as Japanese ships began making their way to Hawaii for RIMPAC, a joint flotilla of eight Chinese and Russian warships had been circling Japan.

Secretary of Defense Lloyd Austin said in March that he intended to close Red Hill permanently and move to a more “resilient” fueling infrastructure by spreading fuel to depots around the Pacific and increasing the use of tankers to fuel ships at sea, taking the fuel closer to potential flashpoints around the region to support U.S. forces and their allies.

However, it’s unclear how quickly the military can or will actually make that transition.

The Wai Ola Alliance, a collection of local activists and former elected representatives in Hawaii that formed last year to press the Navy to keep its promises on Red Hill, is among those that have taken the service to court to ensure that it does.

John Miller, an organizer with the alliance who is also a Navy veteran, said that this RIMPAC will be a major test for the Navy. He also argues that the fact the Navy is doing it without Red Hill demonstrates that it can do its job without the aging facility — and likely could have shut it down long ago.

“Here we are running the RIMPAC exercises using a massive amount of fuel for multiple countries’ militaries here, and so we clearly are able to fill their needs,” Miller said. He argued that the 250 million-gallon facility was designed to store diesel fuel as a reserve for a massive World War II-era fleet of much older vessels.

“They really need to look at RIMPAC and really look at what are the real needs for reserves in the Pacific,” Miller said. “One thing that could be something that can really make this replacement a lot easier is reducing that amount, or at least reevaluating it.”