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Understanding Australia’s strategic moat in the ‘sea-air gap’

The strategic buttress of congested waterways and densely populated archipelagos of the ‘sea-air gap’ has formed the backbone of Australias defence and national security policy since the late-1980s – however, as the region continues to evolve it is critical to understand the role the sea-air gap’ will continue to play in strategic calculations.

The strategic buttress of congested waterways and densely populated archipelagos of the ‘sea-air gap’ has formed the backbone of Australias defence and national security policy since the late-1980s – however, as the region continues to evolve it is critical to understand the role the sea-air gap’ will continue to play in strategic calculations.

Australia’s involvement in the Vietnam conflict at the behest of the US signalled a major shift in the direction of the nation’s strategic policy that continues to influence Australia’s doctrine to this day. Domestic political back lash and a changing geo-strategic environment would see Australia adopt an arguably more isolationist policy, focusing almost entirely on the 'Defence of Australia'.


While Australia's alliance with the US further enhanced the nation's position as an integral US ally  mounting domestic political dissatisfaction, the new Whitlam government and the mounting cost of Australia's involvement in the conflict, combined with rapidly declining US support for the conflict, saw the nation's post-Second World War strategic reality and doctrine begin to shift away from regional intervention and towards a policy favouring the defence of the Australian mainland and outlying territories.

This shifting domestic and regional environment saw the formalisation of the Defence of Australia (DoA) policy in the 1986 Dibb report and the subsequent 1987 and 1994 Defence White Papers, which established the 'sea-air gap' as a strategic 'buffer zone' for Australia enabling the reorientation of Australia's strategic and broader defence industry posture, shifting away from what Dibb identifies: "Until the late 1960s, Australian defence planning and policy assumed that our forces would normally operate in conjunction with allies, and well forward of the continent. We saw our security inextricably linked with the security of others." 

Dibb's report leveraged the 1973 Strategic Basis paper's focus on the nation's isolation to reinforce the concept of the 'tyranny of distance' as justification for reducing Australia's interventionist role and capabilities in the region: "Australia is remote from the principal centres of strategic interest of the major powers, namely western Europe and east Asia, and even those of secondary interest, the Mediterranean, the Middle East and the north-west Pacific."



The 'sea-air gap' encompasses what has long been defined as Australia's primary 'sphere of primary strategic interests' – the narrow maritime sea-lines-of-communication and air approaches to the north of the Australian landmass throughout south-east Asia that served as the nation's strategic, economic and political links to the broader region, through what would eventually become known as the Indo-Pacific. 

Strategic reorientation 

As a result of these shifting geo-political and strategic dynamics, Dibb's late-1980s report suggested a number of force structure changes to the newly formed Australian Defence Force that would focus on protecting Australia's northern maritime and air approaches, known as the 'sea-air gap', through a range of force structure and acquisition programs, including: 

  • Retaining the F-111 force with a minimum update to maintain service capacity until the mid-1990s, while enhancing the capability of the F/A-18 Hornets to receive information from the JORN network; 
    Retain the planned acquisition of the Collins Class submarines to replace the ageing Oberon Class vessels with a focus on "retain[ing] the program for six new submarines but establish a financial ceiling and, if necessary later, explore options for lesser capabilities";
  • Acquire eight light patrol frigates (future-Anzac Class) to enter service from the early-to-mid-1990s, cancel the acquisition of a second fleet replenishment vessel, while cancelling the acquisition of an additional Tobruk Class and the six heavy amphibious landing craft vessels; and
  • Focus on replacing the Air Force's 22 Caribou and 12 Hercules with a fleet of 20 new Hercules-type aircraft.

Additionally, these reductions saw a massive strategic reorientation focused entirely on the north of the Australian mainland, with a focus on directly monitoring the northern maritime and air approaches to the continent, namely the 'sea-air gap', and included: 

  • Raising three Regional Force Surveillance Units for long-range patrols in northern Australia;
  • Redeveloping RAAF Base Tindal as an operational fighter base;
  • Developing three 'bare bases' for the RAAF in northern Queensland and Western Australia to support the rapid domestic deployment of Army units in event of invasion; and
  • Upgrade and enhancement of the Jindalee Operational Radar Network (JORN) to support the long-range air and sea defence of the 'sea-air gap'.

However, the emergence of economic, political and military superpowers like China and India continues to develop as the economic, political and strategic powers at the core of Indo-Pacific Asia. Additionally, Australia has also witnessed the development of the region’s periphery powers including Indonesia, Vietnam and Thailand, each with competing priorities and objectives.

These factors, combined with the rise of both complex asymmetric challenges and the rapid evolution of contemporary weapons systems, including hypersonic weapons systems and multi-domain weapons systems to national security, serve to challenge the established geo-political, economic and strategic security and prosperity of the region – while also effectively serving to reduce the effectiveness of Australia's strategic moat, the 'sea-air gap'.

Responding to a shrinking moat

As the nation embarks on its largest peace time modernisation and recapitalisation of the Australian Defence Force, the 2016 Defence White Paper (DWP) moved quickly to recognise the rapidly evolving nature of the economic, political and strategic status quo of the Indo-Pacific  the DWP correctly identified: "Australia’s strategic outlook to 2035 also includes a number of challenges which we need to prepare for. While there is no more than a remote prospect of a military attack by another country on Australian territory in the foreseeable future, our strategic planning is not limited to defending our borders.

"Our planning recognises the regional and global nature of Australia’s strategic interests and the different sets of challenges created by the behaviours of countries and non-state actors such as terrorists."

Both of these statements clearly identify a shift in the nation's attitude towards the Indo-Pacific, while also recognising that the nation can no longer depend on buffer zones, or strategic moats like the 'sea-air gap', to serve as the basis for protecting the nation and its interests, particularly as the world and Indo-Pacific continue to integrate. 

In particular, the growing capability of China's military, namely advances in long-range strike platforms, have long been identified by Dr Malcolm Davis, senior analyst at the Australian Strategic Policy Institute, as evidence for the nation to embrace a new doctrine of 'Forward Defence in Depth'

Dr Davis explained, "Given the risk a forward Chinese military presence would pose, Australia needs to consider updating its military strategy to one of ‘forward defence in depth’ throughout Indo-Pacific Asia, including into the south Pacific. Australia should not maintain a reactive military strategy that continues to rest on foundations established in the mid-1980s when our strategic outlook was far more benign."

On the back of this, Dr Davis identified the core of the 'Forward Defence in Depth' doctrine, with a focus on three strategic defence objectives, namely: 

  • Deter, deny and defeat attacks on or threats to Australia and its national interests, including incursions into its air, sea and northern approaches;
  • Make effective military contributions to support the security of maritime south-east Asia and support the governments of Papua New Guinea, Timor-Leste and Pacific island countries to build and strengthen their security; and
  • Contribute military capabilities to global operations that support Australia’s interests in a rules-based international order.

"Forward defence in depth would integrate the first objective  essentially the ‘defence of Australia’ mission  with the second objective by giving the ADF a far more visible and regular role throughout maritime south-east Asia and the south Pacific. In doing so, we’d extend our defence in depth far forward, rather than basing the defence of Australia task on being able to defend a comparatively narrow strategic moat that is the ‘sea-air gap’," Dr Davis identified. 

"The third objective  more far-flung operations in support of a global rules-based order  should be prioritised to contingencies across the Indo-Pacific region. The objective of forward defence in depth is to expand our regular military presence and meet any threats that emerge much further from Australia’s shores."

For Australia, a nation defined by its relationship with traditionally larger, yet economically weaker regional neighbours, the growing economic prosperity of the region and corresponding arms build up, combined with ancient and more recent enmities, competing geo-political, economic and strategic interests, places the nation at the centre of the 21st century's 'great game'.

Australia’s security and prosperity are directly influenced by the stability and prosperity of the Indo-Pacific, meaning Australia must be directly engaged as both a benefactor and leader in all matters related to strategic, economic and political security, serving as either a replacement or complementary force to the role played by the US – should the US commitment or capacity be limited.

Get involved with the discussion and let us know your thoughts on Australia's future role and position in the Indo-Pacific and what you would like to see from Australia's political leaders in terms of defining the nation's primary area of responsibility in the comments section below, or get in touch with This email address is being protected from spambots. You need JavaScript enabled to view it. or at This email address is being protected from spambots. You need JavaScript enabled to view it..

Understanding Australia’s strategic moat in the ‘sea-air gap’
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