Guam, America's forgotten speck of an island in the Pacific, is the new front line against China

On a postcard-perfect tropical island in the western Pacific, the United States is bolstering defences at one of its most important military outposts as concern grows over rising tensions between China and Taiwan.

Guam, the largest island in the Mariana chain, is just 50 kilometres long and at most 20 kilometres wide, and boasts a key US Air Force and Naval base.

While there are US bases in Asia closer to the Taiwan strait flashpoint, the island of around 170,000 people is the western-most piece of American territory in the Pacific, allowing a military build-up that would be more difficult for bases on foreign soil.

And the United States is urging allies like Australia to further utilise its bases here.

Its position 2700 kilometres east of Taiwan and about 2000 kilometres north of Papua New Guinea makes its strategic importance hugely disproportionate to its size.

"Guam is almost equal distance between Tokyo, Manila and Port Moresby, it's right in the centre of all three," said Admiral Benjamin Nicholson, Commander of the Joint Region Marianas.

"So anything that happens in this part of world, Guam has been and can be a very strategic location."

And that includes a possible military confrontation over Taiwan, with US aircraft and ships able to reach Asia far faster than from Hawaii or the US mainland.

But while not in close range, Guam's location has one major drawback for the Americans - Chinese and North Korean missiles can reach it.

Just weeks after China fired ballistic missiles over Taiwan to protest against the visit of US House Speaker Nancy Pelosi, the ABC was granted access to Andersen Air Force Base and the nearby US Naval base - America's "forward edge" in the Indo Pacific.

From a forgotten Vietnam War base to a future military hub

Guam played a pivotal role for US Air Force bombers during the Vietnam War of the 1970s. It has been somewhat strategically off the map in the decades since, but China's rapid military build-up is reviving its importance.

Sprawling over 18,000 acres at the northern end of the island, Andersen Air Force base includes stunning stretches of tropical coastline and hosts 8000 service personnel, family members and contractors.

While F-18s roar overhead, on the ground the base looks like small-town America transplanted more than 9000 kilometres from the US west coast, with duplex houses, a school and a mall serving Taco Bell and Subway.

Large areas are reserved for pre-deployment training, with troops from the US mainland and even allied militaries making the long journey to Guam to learn skills for missions ranging from combat to airfield construction.

The days of bombers lined up on the tarmac are gone, with US caution about China's growing missile abilities prompting a rotation strategy that sees them coming and going for specific missions and exercises.

But other activities on the island are ramping up.

There are 5000 marines in the process of relocating to Guam from a base in Japan's Okinawa. The build-up also involves more submarines, ship repair facilities and a planned $1.3 billon missile defence system.

"Having sovereign US territory at this position in the Indo-Pacific ... means we can maintain air superiority from Andersen Air Force base, which is kind of a bedrock the Air Force provides in order to do military operations," said General Paul Birch, the Commander at Andersen Air Force Base.

"Irrespective of who the adversary is or what the tensions are, it gives the United States and its partners and allies a lot more options, and that complicates the strategic calculus for anyone who wants to go against our efforts to keep the Indo Pacific free and open."

Could the US draw Australia into a conflict in the Pacific?

America is doubling down on its allies, hoping their heavy economic reliance on China won't dissuade them from assisting or even joining the US in the event of a regional conflict.

"In the last few weeks I had an Australian command and control aircraft on my ramp, I had an Australian tanker, I had Australian fighters, that were all coming back from yet another exercise in the Indo Pacific region," General Birch said.

Just a day after the US sent two Navy cruisers through the sensitive Taiwan strait in late August, two Australian warships, HMAS Perth and Sydney, docked at the naval base in Guam alongside a Japanese carrier and ships from Canada and South Korea.

The base has long been used as a hub for allies linking the Pacific to Asia, but Australia's increasing reliance on the US - particularly the pursuit of nuclear-powered submarines with reactors that likely won't be built or serviced in Australia - is causing some unease.

Some analysts argue the more Australia is technologically interlinked with the American military, the harder it will be to stay out of conflicts involving the US.

That potentially includes a war with China over Taiwan.

"Is Australia going to get drawn into something? That's really up to Australia and what Australia wants to do," Admiral Nicholson said.

The US military argues better "interoperability" doesn't mean a loss of sovereignty.

"If there are other actors in the region that want to go against international norms and laws, then Australia can speak out against that or take whatever actions the country [feels it] needs to do," Admiral Nicholson said.

The elephant in the room: China's missiles

The US military describes the bases on Guam as a "catapult" for force projection in the region.

But the great rival prompting the need for such force is spoken about only in couched terms.

Asked about increasing interactions between Chinese and US aircraft, General Birch said "sometimes the response we see from various places, whether it be due to a lack of training or simply agitation, aren't always professional".

But the US military is clearly cautious about painting a more detailed picture of the encounters with Chinese forces on and above the seas.

The missile defence plans are a point of sensitivity too.

Guam already has an anti-missile defence system called THAAD, but improving it to give "360-degree" coverage from several types of interlinked systems has become a national defence priority.

China's seemingly successful test of a new hypersonic weapon last year likely made this goal even more urgent.

Chinese state media has warned Guam is within range, and analysts believe the bases would be vital if China attacks Taiwan in the next two decades.

But that comes at a cost for those who call the island their home.

Living under the shadow of war

A critic of the large military presence on Guam, Dr Kuper says its status as an unincorporated US territory means the Indigenous Chamorro people of the island are at the mercy of decision-makers in Washington.

Residents are not eligible to vote in national elections.

But more than 350 years of colonial rule - at the hands of the Spanish, then the Americans, and briefly the Japanese during World War II - has left the Chamorro people in a particularly vulnerable position if Asia descends into conflict.

"When the military talks about missile defence, there's probably no such thing as a zero-leak capability," Dr Kuper said, referring to the possibility for missiles to evade the defence systems and hit their targets.

"For us, one or two leaks through a missile defence system can ruin lives.

"When you have this heightened sabre-rattling, if a mistake happens, Guam may be the first one to go."

With more than a quarter of Guam taken up by military land, residents and local politicians have voiced concern about the environmental impact of deploying more marines and military assets to the island.

But with beach tourism from Japan and South Korea still badly affected by the Covid pandemic, the military build-up is also being viewed as an economic driver.

And cultural links to the US mainland across the vast Pacific ocean remain strong.

Mark Colby, a baseball announcer for Guam's local Major League, is among those celebrating Guam's unique position in the broader United States.

The son of a local Chamorro woman and a Navy officer from Michigan who settled in Guam after being posted to the island, he makes a point to play both the US national anthem and Guam's regional song, known as the Guam hymn, before every game.

"I feel it's my way of honouring our troops," he said.

"There are people here, you know, who recognise themselves as American, because this is American soil.

"But there are some people on this island who don't want to have any association with the US or America, and that's their choice."

- ABC