While most Australians are beguiled by the prospect of this week's presidential visit, it's easy to overlook the fact that President Obama is dropping by for one simple reason: to hike the cost of our alliance.

Though specific details remain vague, the new defence arrangement will involve more extensive training, ship visits and exercises, and the forward deployment of a small detachment of US Marines. It is also likely to cover the prepositioning of materiel, thereby creating a latent staging point for the US military in the Indian Ocean.

The rationale for all this is not hard to discern. While the US has spent the past decade losing wars and squandering power, China has been studiously undercutting US advantages across virtually every realm of policy — economic, diplomatic and strategic. The transformation of Asia's order is well underway, and Washington is playing catch-up. Still, why the sudden interest in Australia? Three reasons stand out.

1. The proliferation of precision strike: over the past two decades, China has accumulated a formidable array of precision-guided strike capabilities, namely long-range ballistic and cruise missiles. These have been woven into an offensive war-fighting doctrine that places an operational premium on their use early and en masse. Since US bases in Japan, Korea and Guam are now at risk of being saturated by Chinese missiles at the outset of a conflict, they no longer constitute an indefinitely reliable basis from which the US can project power.

The countries of Southeast Asia offer no viable alternative; they also lie within range of Chinese missiles. And though their governments clamour for US support whenever China plays rough, they remain unwilling to be prematurely enlisted in US military plans at the risk of becoming a target or arousing Chinese antipathy. Thus, US interest in Australian real estate reflects a simple desire for time and space and a new operational sanctuary beyond China's striking range.

2. America's two-ocean strategy: as US strategists reckon with the scope of Chinese military progress, they are developing an Indo-Pacific strategy for fighting China. In the Pacific, the US Air Force and Navy are fleshing out the fledgling AirSea Battle concept, a war-fighting doctrine aimed at countering China's area-denial strategy from further back. It's a problematic concept, as I've written elsewhere: costly, risky and excessive. Still, by denying China's capacity for denial, the US intends to preserve its options for sea control and power projection, reinforcing its primacy and role as the region's dominant player.

The second aspect of the strategy involves exploiting China's substantial vulnerabilities in the Indian ocean. Such an approach would involve crippling China's economy by blockading or destroying its merchant shipping and energy supplies in war, and, in peacetime, holding them at risk to encourage Beijing's acquiescence. It's a strategy straight out of Washington's World War II playbook. Indeed, the mere presence of a powerful allied naval contingent along China's sea-lines would require Beijing to divert considerable resources away from its coastline, much as it did with Japan in the 1940s, thereby diluting the singularity of Chinese efforts in the western Pacific.

This is where Australia would come in: as a central point between the two theatres, a hub to reduce transit times between each end, and a base supporting an expanded commerce raiding or blockading campaign against China, most likely in the western reaches of the Indian Ocean, beyond China's naval reach. 

3. Keeping Canberra on the leash: the third motivation for an expanded US presence in Australia is political. Washington is keenly aware of the centrality of China to Australia's economic wellbeing. American strategists also recognise the extraordinary geographic advantages that Australia enjoys — a shoulder each in the Pacific and Indian Oceans, its back to Antarctica and shielded by a long archipelago. They understand what many Australian fail to see: that Canberra could, with some clear thinking and a substantial yet sustainable increase in spending, defend itself without becoming entangled in the power-politics of Northeast Asia. And they are determined to prevent that from happening.

In this regard, Washington is being clever. It is taking full advantage of Australia's current strategic dependence, locking in Canberra's political and military support, thereby minimising the likelihood of any future Australian defection.

Photo by Flickr user Turkinator.