Is sea denial without sea control a viable strategy for Australia?

In his provocative new book, How to defend Australia, Hugh White suggests a strategy of ‘sea denial’ for Australia’s defence. To protect a large island from threats posed by geographically distant potential enemies, this makes a lot of sense. Specifically, White argues that Australia can adopt sea denial without seeking ‘sea control’. That, together with his contention that ‘the contest between a force trying to control the sea and an adversary trying to deny it is very unequal’, underpins much of his book. He believes this means that sea denial will be a comparatively cheap and achievable policy for a middle power in a region dominated by rising great powers.

But White has conflated two very different strategies of sea denial, suggesting the benefits of one can be achieved at the costs of the other. By examining the strategy White is actually proposing, it’s also possible to understand the truly radical nature of the methods he believes can be used to achieve it. He may be correct, but the proposal relies on modern technology fundamentally altering existing strategic principles—and it’s not certain that’s the case.

What is sea control?

The phrase ‘sea control’ is frequently used by those discussing maritime strategy but, like its cousin ‘command of the sea’, it’s meaning is very difficult to pin down. Essentially, sea control is ‘the ability to use the sea in reasonable safety’.

Sea control is rarely, if ever, absolute, and is heavily bounded by time and space. This matters less than is commonly supposed. What’s the benefit of controlling an empty bit of ocean? What you really need is enough control to achieve your ends. A classic example is Operation Pedestal, a famous Malta convoy in World War II. The British never achieved absolute sea control, or anything approaching it. They did, however, have sufficient control over the specific area of sea for the time that the convoy was passing through (just).

Sea denial is related to sea control, but it’s not a direct mirror. White is correct in pointing out that a power exercising sea control will generally be able to deny use of the sea as well. However, the shifting and relative nature of these concepts makes this less clear-cut than is generally imagined. Looking at the two different types of sea denial which White conflates will demonstrate this more clearly.

Limited sea denial

The first type of sea denial is what I’ll call ‘limited sea denial’. It’s the form most commonly associated with the term, and classic examples include French guerre de course (commerce raiding) in the 18th century, and German U-boat warfare, which White uses in his analysis.

The term sea denial in this context is a misnomer. This strategy does not intend to deny the enemy use of the sea at all. Instead, it seeks to increase the cost of their use of the sea to limit the benefits they can gain from it. It can do so through numerous channels, most notably by destroying trade, which impacts the domestic economy and war effort, or by interrupting supply to military forces overseas.

France and Germany adopted this strategy because they couldn’t challenge British sea control directly. They accepted that the results would be limited. Even at the height of the Battle of the Atlantic in March 1943, the Germans were sinking less than 3% of merchant ships convoyed. White is perhaps correct in concluding that this form of sea denial has become ‘relatively easy’, but that should provide little comfort for those relying on it for territorial defence.

This strategy was available to weaker maritime powers such as France and Germany because of the methods used to carry it out. As Admiral Stansfield Turner remarked, ‘Sea denial [or at least limited sea denial] is essentially guerrilla warfare at sea. The denying commander strikes at a time and place of his choosing to achieve maximum surprise; he does not have to stand his ground toe to toe with the enemy, but instead hits and runs.’

This strategy doesn’t rely on the denying force having any serious degree of sea control. Instead, they can use comparatively limited forces to achieve results by exploiting areas where their enemy’s sea control is weakest, and avoiding areas where it is strong. This is seen in the U-boat campaigns, with their relatively high levels of success against independently sailing merchantmen, and low success against heavily defended convoys.

Limited sea denial operations are unequal in nature. Defence of trade, in particular, is challenging because the power seeking to use the sea has to have sufficient control across a huge geographic area and for long periods of time. The problem for White’s argument is that this type of sea denial bears little resemblance to the type he’s actually talking about.

Defensive sea denial

White is generally describing a concept I’ll refer to as ‘defensive sea denial’, which entails trying to use the sea as a barrier to enemy aggression. In contrast to limited sea denial, defensive sea denial requires a very high level of sea control. For the strategy to work, the denying force needs to be stronger than its enemy everywhere (within the region of operations) all of the time. It’s no good being able to defend half of your coastline, or to do so whenever your forces are deployable.

In marked contrast to limited sea denial, to achieve defensive sea denial you must be able to destroy your enemy’s strongest forces. White is correct in suggesting that sea denial in this context is tactically and operationally offensive, and therefore potentially benefits from any implicit advantages of that posture.

However, the nature of defensive sea denial negates most of these advantages. There’s very limited scope for the denying commander to pick the target, time or place—or to decline combat. By contrast, the commander of an invasion flotilla would know exactly the geographic space they needed to command, and the time they needed to command it for, allowing them to marshal their forces accordingly. For these reasons, defensive sea denial displays little of the relative advantage over sea control that White’s thesis relies upon.

Defensive sea denial is a very common strategy and an implicit part of the strategies of maritime states such as Britain or Japan. We don’t generally recognise this, because it is subsumed into their wider strategy for more general sea control and is carried out by those forces. Large continental powers, such as the Soviet Union and China, have used it to defend their coastlines and to support their powerful land forces.

The defensive sea denial required by maritime states generally needs to be both more absolute and more immediate than that of continental powers. If, as was historically the case with Britain, sea denial is the primary line of the state’s defence, then the strategy needs to be successful, and to work fast, to prevent enemy forces from landing in any serious number.

By contrast, continental powers can rely more on their land forces to continue to contest any attack, meaning sea denial can be less absolute and can continue for as long as the invading force requires support from the sea. The position of Australia, as outlined by White, is far more analogous to that of the maritime states. If sea denial is to be Australia’s premier self-defence strategy, it will need to work, and do so quickly.

The problem is that defensive sea denial has historically been considered difficult. The issues were explored at length in the British debates about invasion in the second half of the 19th and first half of the 20th centuries. These reinforce how difficult achieving a high level of sea denial can be, even for a power exercising general sea control.

The British constantly struggled with how they’d combat a sudden invasion attempt that would allow France, or later Germany, to concentrate its naval forces sufficiently to gain enough temporary sea control over sections of the English Channel or North Sea. This took its most concrete form on the outbreak of World War I, when even the vast power of the Grand Fleet didn’t provide sufficient security for Britain to deploy immediately all six of its regular army divisions to France.

Concerns about a German invasion continued throughout the war, and the inability of the Royal Navy to prevent raids on coastal communities caused huge frustration within the service and beyond. The inability of a force as powerful as the Royal Navy to exert defensive sea denial during World War I underscores how difficult it is to guarantee being strong enough everywhere, all of the time.

Sea denial without sea control?

White argues that a sea denial strategy can be achieved without the need for sea control, and at a fraction of the cost. There are two broad ways in which this can be done. The first is through the use of asymmetric forces, usually some form of flotilla. Arguments of this type have been around for centuries and include elements of the French Jeune École, the Soviet New School of the 1930s, and Chinese strategies of the early communist era.

Certain points are common to most of these strategies. First, they’ve been adopted by states that are primarily land powers seeking to protect their coastlines. That meant that they didn’t need to offer the same level of ‘absoluteness’ required by a maritime power.

Second, they’ve sought to use numbers to counteract the relative weakness of individual units. Individual units of the flotilla couldn’t have competed against major enemy combatants, but together they offered the potential to overwhelm them.

Third, they’ve challenged across multiple domains (this will become more relevant later).

Finally, and perhaps crucially, they’ve been acknowledged as being limited in their effectiveness. They were adopted by land powers facing maritime rivals, and even China and the Soviet Union rapidly moved away from them towards more conventional maritime strategies.

It’s also worth pointing out that for these strategies to be effective as defensive sea denial, they still require a considerable level of sea control. An effective flotilla may not have been able to exercise sea control on the open ocean, but it would have done so in littoral waters.

Control of one domain or three (or five)?

The other way in which sea denial can be carried out without sea control is far more radical and is the one White seems to be proposing. This approach exploits a crucial variation between all types of sea denial and sea control, namely that sea denial can theoretically be achieved through superiority in one domain only.

To use the sea, it’s necessary to have sufficient command of three, or perhaps now five, domains for the specific time and space. By contrast, if the denying power were able to establish a high level of command of one domain, say the subsurface domain, it could, theoretically, successfully deny the attacking power the use of the sea. This scenario could result in mutual sea denial.

Probably the closest historic example we have of this took place for periods in the Mediterranean in World War II. German and Italian airpower was matched by British strength in the other two domains, making it difficult for either side to effectively use the sea.

But dominating a single domain is difficult. Forces operating in the different domains are invariably self-supporting, and it’s extremely challenging to have a very high level of command of any one domain without being able to contest the others.

Germany’s experience in World War II demonstrates this clearly. Some of its most successful operations involved a combination of surface, subsurface and air forces. The most obvious example was the destruction of convoy PQ17 when the threat of a German surface raider forced the convoy to scatter, limiting Britain’s ability to provide sufficient command of the other domains. The results were devastating.

More generally, Germany’s inability to even contest the surface and air domains in the Atlantic made anti-submarine warfare far easier for the Allies. The reality of the requirement to at least contest other domains to establish dominance in one also underpinned the Soviet bastion strategy, which is arguably now being replicated by the Chinese.

White’s conflation of two very different types of sea denial raises questions over his analysis of the relative ease, and cost, of such a strategy. That suggests there’s scope for further debate over its relative primacy in the wider national strategy.

The same could be said for White’s conclusions about the methods to be used to achieve sea denial. The novelty of the concept of providing sea denial by dominating only one domain is worth highlighting and raises questions about its initial feasibility and the advisability of relying upon it.

Ultimately the answer to this, in large part, rests on the assessment of the capabilities of modern technology. However, given the scale of the uncertainty over such capabilities, and the importance of the task, it’s not clear that it’s appropriate to rely so heavily upon such an approach.