On Obama's decision to scrap America's eastern European missile defence sites, The Age says '(i)t is not yet clear what that means for plans for the Asian sections of the system and joint experimental work being carried out by Australia, Japan and the US.' I'm not aware precisely what trilateral 'experimental work' is being carried out, but I think this decision would have almost no negative impact on it; indeed, it's likely to be positive.

That's because America's Asia Pacific missile defence architecture is built largely around the AEGIS combat system and the SM-3 interceptor. Both AEGIS and SM-3 are based onboard US Navy and Japanese navy destroyers; AEGIS will be fitted to Australia's new Air Warfare Destroyers (AWD; below) and SM-3 might become part of the armoury too.

Given that Obama's plan is to move away from ground-based radars and interceptors (of a similar kind to those already deployed in Alaska and California) and to instead protect Europe with AEGIS and SM-3, it actually represents a boost for that system, and thus could actually speed technical and tactical developments that might eventually find their way into the Asian theatre.

At the strategic level, this decision also reinforces a trend toward cooperative missile defence. Here's the key part of the Pentagon statement from GEN James Cartwright:

And so this enhanced architecture we put together associated with Europe is also an architecture that is globally deployable and is the same architecture that you would find if you went now to Japan, South Korea, facing the North Korean threat and the ground-based interceptors that defend against that. We're also looking at this architecture with an initial deployment that occurred earlier this year with the ground-based radar that went into Israel. So this is an architecture that is globally exportable...

'Globally deployable' is the key phrase for me. What we're seeing is the next stage in the development of a global missile defence coalition, which has been made possible by the fact that missile defence technology has become steadily better and cheaper, and is thus being taken up by second- and third-tier military powers.

It remains to be seen how that coalition will develop in an operational sense. Countries all over the world will have similar systems that can theoretically be knitted together into a truly multilateral missile defence system. Many elements of that system — ship-based, space-based and road mobile — will be deployable to world hot spots at short notice.

But the political barriers to a globally deployable missile defence coalition are huge and potentially very tricky for Australia, particularly given Chinese sensitivities. My concern is that Australia may allow its defence policy to define its foreign policy. The recent Defence White Paper said nothing definitive about participating in missile defence, but once we have our AWDs, its going to be hard to stay out of it, given that (to my understanding) the technological fixes required to allow the AWDs to 'plug and play' in America's missile shield are fairly minor and cheap.

Before we take that leap, we need to have a discussion about whether it is really in our interests to take part.

I'll be discussing these issues with Mark Colvin this evening on ABC Radio's PM program.

Illustration courtesy of the AWD Alliance.