The attack started at about 8:50 a.m. Sunday off Pyramid Rock on Oahu’s Windward coast.

Thousands of Marines, sailors and military personnel from various nations prepared to seize an airfield from an enemy in the fictional country of Griffon.

A pair of F/A-18 Hornet fighter jets roared over the coastline, providing real-time information about the enemy to command staff, and simulated delivering fire on the ground before multinational forces made landfall in an amphibious assault.

Twenty-one assault amphibious vehicles, or AAVs, approached the beach in waves of about four, deploying from the Royal Australian Navy’s HMAS Adelaide, positioned about 1.2 miles from the shoreline, and Indonesia’s KRI Makassar.

It was the culminating event for U.S. Marines participating in the 26th Rim of the Pacific exercise, which ends Thursday. The Marines allowed the media and military families to observe the exercise from Marine Corps Base Hawaii.

The operation was run by Combined Task Force 176, one of the largest task forces in RIMPAC, comprising 17 ships, 30 aircraft and 7,000 soldiers, sailors and Marines from 10 different countries.

Royal Australian Navy Commodore Ivan Ingham, task force commander, said the exercise demonstrated a “force projection” from sea to shore with the aim of promoting relationship-building, cooperation and trust among the different participating nations for missions such as disaster response crisis, humanitarian assistance and maritime security.

The simulated attack was the largest amphibious exercise during this year’s RIMPAC, said Col. Michael Styskal, commander of the 3rd Marine Regiment and the Marine Air-Ground Task Force-Hawaii, which conducted the amphibious landing.

“This is a very complex operation to get ships and amtracs and aviators and planes all into one spot and a very tight area,” Styskal said, using another name for the AAVs, also known as amphibious tractors. “We’ve been planning this for a number of weeks, and at the end of the day, it went very well.”

He said the amphibious assault was the conclusion of a fictional war that had been going on for five days, and it demonstrated how such an operation would take place in the real world, first with the preparation of the battlefield by aircraft, then with amphibious combat power moving onshore and finally additional assaults by helicopters.

One challenge for the multinational force was the language barrier, but “amphibious language” is common across the different nations, helping in operations, he said.

The forces in the amphibious landing included personnel from Australia, Chile, Indonesia, Japan, the Philippines and South Korea.

Earlier this month the team of multinational forces spent about 10 days training to communicate better and smooth over differences in tactics and procedures, he said.

“We’re stronger together” going into a humanitarian assistance and disaster relief operation, he said. “If we tried to do it all separately, we wouldn’t be as connected.”

In Sunday’s scenario the RIMPAC coalition forces ran a humanitarian assistance and disaster relief operation after Griffon was hit by a magnitude-6.9 earthquake. Forces in the country hostile to the government began attacking Griffon’s military to capitalize on the instability and were partially successful in overtaking the airfield, which would have denied RIMPAC forces aerial access to Griffon.

Combined Task Force 176 was ordered to launch an amphibious assault at Pyramid Rock and establish a station for additional coalition forces in support of the government.

With a maximum speed of about 8 mph at sea, the amphibious assault vehicles advanced with a slow determination, ferrying 306 Marines, sailors and other military personnel to the beach.

Explosions went off as the forces scrambled, boots on the ground, across the beach into the brush.

A drone flown by the Marines circled overhead, and two CH-53E Super Stallion helicopters departed from the HMAS Adelaide carrying 48 military personnel to be dropped off inland. Following them was a CH-53 helicopter carrying an M777A2 155 mm howitzer weighing 9,000 pounds, also to be placed inland.

Maj. John Hinton, a fighter pilot with the Marine All-Weather Fighter Attack Squadron 533, attended the event as a spectator and said he enjoyed seeing the different components of the Marine Air-Ground Task Force working together.

“It’s very rare that you get to see the MAGTF in action,” he said.