Military commanders from Japan, Australia, the Philippines and 20 other mostly Asia-Pacific nations huddled around a large tactical map, poring over satellite images in readiness for an amphibious raid on Hawaii's most populous island Oahu.
Although only a drill, it represented a glimpse of cooperation and integration among non-Chinese amphibious forces in Asia that the United States is belatedly encouraging.
A senior U.S. official told Reuters the-first-of-its-kind gathering also signifies a nudge towards containing China, as Beijing grows increasingly assertive in pushing its territorial claims in the South China Sea.
The shift has left supporters of engagement with China "under pressure", said the source, who declined to be identified because he was not authorized to speak to the media.
Early on Tuesday, the foreign amphibious commanders participating in the PACOM Amphibious Leaders Symposium (PALS), boarded Osprey tilt rotor aircraft at Hickam air base, near Honolulu, for a 20-minute ride over the tropical seas around Oahu to the amphibious assault ship USS Essex and other vessels for a demonstration of American marine muscle.
US Navy handout photo of the USS Tortuga in Subic Bay.
"I don't think China can match the complexity," said Martin Sebastian, head of the Maritime Institute of Malaysia, in the hangar deck after a tour of the 40,000 ton, 266-meter Essex.
A U.S. spokesman said China was not invited to the meeting because doing so would have contravened a law prohibiting military-to-military exchanges with China at such events.
China joined in U.S.-led Rim of the Pacific (RIMPAC) naval exercises last year with more than 20 countries, but was limited to things like humanitarian relief and search and rescue operations.
Tuesday's exercise had only a military objective; to land a marine units on a beach by boat and helicopter and destroy the fictitious training camp of an insurgent group.
The drill, involving Ospreys, Harrier jump jet aircraft, armored vehicles, B-52 bombers and hovercraft, follows a two-day visit to China by U.S. Secretary of State John Kerry that was dominated by concerns about Beijing's territorial ambitions.
Recent Chinese reclamation work has stoked tensions in the South China Sea, where Beijing is building man-made islands around seven reefs in the Spratly archipelago that are also claimed by the Philippines and Vietnam.
With a force of around 12,000 marines that it can rapidly expand in times of conflict, China, say military experts, represents a formidable potential foe.
The United States maintains a presence of some 80,000 troops, almost half its strength, in Asia, most on Japan's Okinawa island at the edge of the East China Sea.
Better integrating the amphibious operations of non-Chinese forces in the Asia-Pacific represents an arduous challenge. Capabilities vary from country to country, gear, including communications, is not interoperable and funding is scarce.
"Capabilities haven't developed as quickly or as fully as they might," said Grant Newsham, a former Marine liaison officer to Japan's Ground Self Defense Force, who attended the meeting.
"The Symposium will hopefully coalesce these ongoing but somewhat disjointed efforts towards amphibious capability."
Inter-regional rivalries are another hurdle to cooperation.
For example, one participant, who asked not to be identified, said cooperation between Japan and South Korea, which has about 25,000 marines, was impossible because Seoul might one day have to defend territory also claimed by Tokyo.
For some checking out the U.S. military hardware, America's enthusiasm to forge more capable amphibious forces in the region could provide a more immediate benefit by helping prepare for natural disasters such as super typhoon Haiyan, which killed more than 6,000 people in the Philippines 2013.
"It will help enhance the capability we should have," said Alexander Lopez, a Philippine vice admiral. The U.S. "is a big brother for the region".