Could Australia defend itself independently from direct military attack by a major Asian power like China? That’s the key question I set out to answer in How to defend Australia. My answer was a cautious ‘yes’.

That answer was based on two judgements. The first was that Australia’s key strategic objectives—the things we most needed our armed forces to be able to do in order to defend ourselves—could be achieved with what I called a military strategy of maritime denial. The second was that we could achieve maritime denial with forces which we might, at a stretch, be able to afford.

Two kinds of argument can therefore be mounted against my conclusion. One is that maritime denial is not sufficient to achieve our key objectives. The other is that it’s not as easy, and hence not as affordable, as I had supposed.

Both these arguments have been put forward in the extended discussion of my book which The Strategist has been kind enough to host since it was published in July. The first was set out most persuasively by my old friend and sparring partner James Goldrick, and the second by Richard Dunley.

Dunley focuses on sea denial, which is an essential element of maritime denial, so if his argument about sea denial is right then my strategy of maritime denial is doomed. He subjects my arguments in favour of sea denial to a searching analysis. He is well placed to do this as a naval and diplomatic historian who has researched deeply on these and related issues, and I’m grateful to him for taking the trouble to critique my ideas so thoroughly.

His argument that sea denial is harder than I portray rests on two ideas. The first is that to be effective in defending against a lodgement of enemy forces—as opposed to just disrupting trade, for example—sea-denial operations need to cover the whole theatre all the time, to ensure that the adversary cannot slip through a gap. The second is that achieving sea denial at this level is extremely hard, and in particular that it would require the establishment of sea control.

I think both ideas are wrong. It would require an immense effort to defend all sectors of our air and sea approaches equally and sufficiently to ensure that no adversary forces could ever approach our coast. As Dunley says, even the Royal Navy at the height of its power could not guarantee that German forces would not raid Britain’s coastline—a point Winston Churchill made in a famous wartime speech in June 1940.

But that sets the bar too high. The question is not whether we can be sure of stopping every attack, but whether we have a good chance of stopping the most serious assaults. Small raids are always possible, but they don’t matter so much. The bigger an assault, the easier it is to spot and the more vulnerable it would be to interdiction.

Moreover, the task of detecting an attack as it approaches and concentrating our forces against it is easier than the historical analogies suggest. We have—or should have—much better wide-area surveillance than was available in World War I and our adversary must advance a lot further from its home bases than the width of the North Sea.

More broadly, the question is not whether we can be sure of stopping an adversary, but how sure the adversary can be that we cannot stop them. As I said in How to defend Australia (pp. 91–92), the underlying aim of Australia’s defence posture should be to raise the costs and risks to an adversary of attacks against Australia to the point that they exceed any potential benefits. This doesn’t require us to be certain of stopping them. We only need to make them believe that we have a good chance of doing so.

Dunley’s second argument—that to achieve sea denial is much harder than I suggest—also relies too much on historical analogies. As I argue in How to defend Australia (pp. 101–102), until the end of the 19th century sea denial did require sea control, because only warships could achieve sea denial beyond the range of coastal guns.

But since the development of wide-area surveillance systems and sea mines, aircraft, submarines, torpedoes and guided missiles, it’s become easier and easier to find and attack an adversary’s ships far from shore without using ships of one’s own.

It’s far from clear that surface ships have any cost-effective role to play in multi-domain sea-denial operations. So, achieving the sea control required to allow us to operate ships in the combat zone would not materially contribute to sea denial. In fact, it would detract from it by diverting resources from the core task.

Arguments about future operations are always speculative, especially when the last major maritime conflict ended nearly 75 years ago. But in discussing the future of sea-denial operations we have a major contemporary case study to guide us.

China’s anti-access/area-denial posture works exactly the way I envisage an Australian maritime denial strategy working. And it seems clear that this posture has been very effective in raising the costs and risks to the US of deploying forces by sea against China. It’s not clear to me why this can’t work for us.

James Goldrick makes a different point. He rejects maritime denial as a strategy for Australia because it does not provide a means to defend our trade and especially our fuel imports. It’s an extremely important point.

He’s right that successful interdiction of our trade would be a major strategic disaster for Australia. And he’s right that only a military strategy emphasising sea control would allow us to defend against that disaster.

The question Goldrick leaves unanswered is how such a strategy could be implemented. What forces would be required to give Australia a credible independent capacity to defend even the smallest proportion of our most vital trade? How much would those forces cost?

I think it’s clear, for the reasons I set out in How to defend Australia, that there are no realistic answers to these questions. If the defence of trade is essential to our strategic independence, then strategic independence is beyond us.

To Goldrick and others that doesn’t matter. They don’t believe we need to worry about strategic independence. They are content to assume that we’ll never face a major power alone, because we will always find powerful allies to help us.

I will explore and contest that assumption in my next post.