The stronger China becomes, the more useful the bases will be. At first they'll probably be out on a limb, merely helpful to Beijing and distracting for its opponents, not powerful centres for projecting military strength.

That could change.

The biggest worry for Australia is not Chinese armed forces setting up far out in the Pacific, though that would complicate our defence planning quite enough. Instead, what must keep our planners awake at night is the risk of the Chinese military appearing much closer to home, in Papua New Guinea and, above all, East Timor.

China this week made a curiously overambitious attempt to rope 10 Pacific island countries into a deal that would have put all of them on the path towards military alignment with it. Embarrassingly, it failed utterly.

But that just puts Beijing back to the far more realistic task of working on these countries one by one - by building up economic influence, offering bribes to politicians and maybe helping them to subvert democracy and stay in office. None of that is unfamiliar to Chinese leaders, much less distasteful to them.

We can do our best to stop this, but our power is so much weaker because we will not and should not bribe. We will rely on trying to match China economically in these little countries and doing what we can to appear as trustworthy old friends.

The strongest factor on our side will be the unwillingness of people of Pacific islands to be part of a military competition.

But it is just unrealistic to expect that relentless attempts to buy leaders and rig politics will ultimately fail.

So we should assume the bases are coming. What will they mean to us?

The answer depends on location: the closer they are, the bigger the worry.

What follows will seem like fantasy to some readers, but it is exactly the sort of stuff that's thought about in military planning, especially for the long term.

First a principle: military power fades with distance, like the warmth radiated from an electric heater.

Close to its own territory, China's military power is already fearfully hot, maybe too hot for even US forces to withstand. But China can't project much strength into the central or south Pacific.

Out there, it is basically down to using submarines, which certainly present a danger but nothing like the firepower of the masses of missiles and aircraft ranged along the Chinese coast.

Setting up a base away from home territory is like using an extension cord, providing a socket away from the wall for another heater, probably a small one. A Chinese base in the Solomon Islands, for example, could host missile forces that would radiate their heat across the Coral Sea towards Queensland.

But don't forget the cord; if it's cut, the heater quickly stops radiating. If the base no longer receives supplies - weapons, fuel and so on - along a line stretching back home, it becomes ineffective when it uses up what it has in stock.

For at least the next decade, China could not hope to secure wartime supply to bases out in the Pacific. It's just not strong enough there to face the US Navy and Air Force.

Nonetheless, a remote base stocked with ground-strike and anti-ship missiles could still threaten enemies. Even if it didn't use the weapons, instead presenting a persistent threat, it would be a distraction that would have to be neutralised somehow.

In peacetime, the base would be used for surveillance.

A Chinese base in Papua New Guinea would be an even greater problem for Australia than one in the Solomon Islands, because it would be closer. It might threaten most of our northern defences, such as airfields.

Still, if Indonesia did not allow Chinese cargo aircraft to fly through its airspace, that base would also need a supply line running through the Pacific. If a large supply quantity was needed, it would have to go in ships, which would definitely require a Pacific route.

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That brings us to East Timor, a country that our defence planners must be thinking about carefully.

It's also close to our defences. Moreover, it can be supplied through the South China Sea, which China could hope to control, and through straits in the Indonesian archipelago that are available for international use.

Straits are ideal lurking grounds for submarines trying to intercept ships. That's one reason why we need more and better subs as soon as we can get them.

China's ability to sustain powerful bases elsewhere with oceanic supply will rise as it becomes stronger, especially if it can ultimately push the US to the far side of the Pacific.

A lot depends, too, on whether surface ships will be survivable in the decades ahead, as satellites track them and missiles stand ready to sink them.

Instead of bases, another way to project power a long way from home is to use aircraft carriers.

At the time of writing, China is reportedly ready to launch its third aircraft carrier. This will cause a great hullabaloo, but it's not an immediate problem, because China is still learning the very complex business of operating aeroplanes at sea.

We will have to be ready for that threat when it finally matures, however.

Most importantly, our defence policy makers must think carefully about how we should shape our military to be ready when and if ground-based Chinese forces set up on our doorstep.

National defence could suddenly become much harder.