After a decade spent mostly fighting in deserts and mountain regions, the US military and its allies have been gearing up for future challenges by practising assaults on coastal areas.

A mythical nation is under attack by a belligerent neighbour. The US and its allies are deployed to save Amber from the invading forces of Garnet.

For the teams coming off the amphibious assault ship the USS Kearsarge, the mission was to push the intruding forces out.

In reality they arrived on the beaches and grounds of Camp LeJeune, a sprawling Marine Corps base in North Carolina.

Searching the waterways nearby for Garnet-affiliated "pirates" were US Navy Riverine units, based on small boats often visually associated with the Vietnam War.

The scenario was part of Bold Alligator, an 11-nation training exercise involving upwards of 19,000 troops.

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The US military is beginning the process of changing its force structure to meet new threats

While the scenario may have been a fiction, the reality for all involved is a shifting military focus, as the US and other participating nations are increasingly watchful of coastal areas of the Middle East - in particular Iran - and countries like China and North Korea in the Pacific.

The Bold Alligator exercise involves scenarios of mine warfare, fighting in shallow water and fending off attacks from smaller boats; methods known to be familiar to the Iranian Navy.

Capt Dorian Jones, commander of the USS Kearsarge, was quick to point out other uses for the training, such as responding to the Haiti earthquake two years ago.

"Amphibious operations encompass a number of different operations - humanitarian assistance, disaster relief. Amphibious forces are flexible and capable, and they flex to a variety of missions."

'Back to basics'

Bold Alligator has been under way since the beginning of February, played out across Virginia and North Carolina in what US military officials say is the largest amphibious-focused training mission in over a decade.

The outline of the exercise is not far removed from the depiction in films like Saving Private Ryan, or even from the reality of the World War II Normandy beach landings.

Bold Alligator has taken months of planning and is a joint-forces operation between the US Navy and Marine Corps.

Participating in the exercise are 25 ships, including the aircraft carrier USS Enterprise and the lead assault ship USS Wasp.

Troops include sailors and Marines from several "partnership" countries such as the UK, Canada, France, Australia and the Netherlands.

According to Adm John Harvey, commander of US Fleet Forces, the purpose of Bold Alligator is "to get back to basics" in terms of the ship-to-shore method of fighting that the recent missions in Iraq and Afghanistan rarely required.

Speaking in Washington as Bold Alligator was getting under way, he said: "It was really instructive to me when we opened this thing up to our coalition partners, they jumped on it.

"I've got a French big-deck under way out there now, with a lot of French Marines embarked who are taking this exercise with great seriousness.

"Gen Heljik's [a US Marine Corps commander] got a couple hundred Dutch Marines who came over here for this.

"We have 11 nations playing and playing hard, like the Canadian minesweepers, and they're making these decisions to participate at a time when their fiscally-constrained environment is far, far more significant than ours."

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The US military focus is shifting to coastal areas of the Middle East

From the amphibious assault ship USS Kearsarge, troops from the US, UK and Canada were grouped together and then sent out in LCAC landing crafts and V-22 Osprey - a helicopter-plane hybrid - as one part of the 12-day exercise.

Before flying off on 6 February, the would-be D-Day of the war games, Maj Chris Samuel of the British Royal Marines said: "This is essentially restoring our amphibious credentials and it's a unique opportunity really, to participate in a multinational exercise with our closest allies.