Recent statements by Defence Minister Richard Marles ^[1] and Prime Minister Anthony Albanese ^[2] have flagged an early outcome from the defence strategic review ^[3]—the intention to acquire an ability for Australia to hold an adversary at risk at long range ^[4]. A range of capabilities will be required to locate, target and strike an adversary’s ships, submarines and aircraft entering Australia’s maritime approaches, typically south of the Indonesian archipelago. ‘At long range’ may also include the possibility of interdiction north of the Indonesian archipelago, as many commentators have been suggesting. Both options are a long way up the escalation chain and would invoke some complex legal and practical issues, not least with our neighbours.

Attacking or, more importantly, deterring an adversary would require long-range maritime strike missiles and platforms to carry, target and launch them. These platforms could be land based or carried in our aircraft, ships and submarines. Each platform has strengths and weaknesses.

Aircraft have the virtue of rapid turnaround times, but they are an overt platform whose deployment could be seen as escalatory and attract a pre-emptive response. They would be operating at long range, with limited time on task. This could be a crucial limitation—for example, if time is required to resolve a confused targeting situation.

Surface warships are another overt platform, though they can loiter in an area for extended periods and have lower presence implications. They are expensive to crew and to own and are vulnerable to attack. The number of strike missiles carried would be limited by the overall magazine capacity and the need for the ship to carry self-defence missiles. Reloading would require a return to a suitable base and could take several days, depending on the geography.

Submarines ^[5] offer some unique capabilities. Their stealth, long range and endurance provide a maritime strike platform able to linger on task for weeks, undetected, observing and reporting as events unfold. They are expensive to build and own. The submarine holds the tactical initiative and can spend time resolving any targeting issues, without exposing itself. This gives the government an option to strike with the benefit of tactical surprise or to leave the scene without escalating the situation, as would occur by deploying an overt platform. Submarines inject the maximum amount of operational uncertainty into an adversary’s calculations.

Submarines also carry long-range, wire-guided, active-homing torpedoes with large warheads that can disable or sink even the largest of ships. And they are the best weapon for use against an adversary’s submarines. The torpedo’s discrimination and lethality ^[6] probably make it the weapon of choice in many scenarios.

The Royal Australian Navy’s conventionally powered Collins-class submarines can carry a mix of 22 full-length weapons ^[7] (torpedoes and/or missiles, depending on the mission). Reloading requires a return to base and could take weeks.

Nuclear-powered submarines, which Australia is planning to acquire through the AUKUS pact with the UK and US, have the advantage of greatly improved mobility, stealth and survivability. They have a shorter transit time to reload than a surface ship, and typically carry many more full-length weapons than conventional boats (the UK’s Astute-class SSNs can carry 38).

Given their covert profile, submarines offer the greatest level of deterrent, creating a question mark in an adversary’s mind, as Marles has observed ^[8]:

And at the very heart of what makes submarines so special is stealth.

It is these unique attributes—the fear a submarine may be lurking ahead, undetected and ready to strike—that gives a potential adversary pause.

As I have said in the past, when we talk about buying a submarine, what we are ultimately buying is a question mark in an adversary’s mind.

And the importance of that question mark should not be underestimated.

Targeting is a difficult part of the maritime strike equation. It’s not easy to hit a moving target in a maritime environment, which is often crowded with neutral or friendly vessels and has land masses nearby. Delivering a successful strike will require a significant Australian communications, intelligence and surveillance capability.

In a recent article, I discussed the need to avoid a gap ^[9] in Australia’s sovereign, operational submarine capability during the transition to SSNs. The key adjectives here are sovereign and operational. The risk that we will face a submarine capability gap has led some commentators to suggest ^[10] we should acquire long-range B-21 bombers ^[11] from the US.

Details on the B-21 ^[12] are as scarce as they are highly classified. The aircraft was only shown in public for the first time ^[13] over the weekend and is still under development. Its first flight was recently delayed until 2023 and initial operational capability in the US Air Force is expected in the 2030s. It is designed as a highly stealthy aircraft able to penetrate defences and attack an adversary’s homeland. It can be armed with conventional or nuclear weapons and will be very expensive. Any issues arising from adapting it to maritime strike are not known.

The timing for achieving a fully operational capability in a maritime strike role in the Royal Australian Air Force is hard to estimate given the B-21’s current status and the delays already experienced. The 2040s, or later, seems reasonable.

Despite its tactical stealth, the aircraft is an overt platform: they require a base capable of supporting them whose operations would be subject to local and overhead observation as they are prepared and launched.

Deploying strike aircraft in a situation short of all-out hostilities is likely to be seen as an escalatory step. Deployment north of the archipelago would require access to a third nation’s airspace. There’s little room here for the question mark the minister seeks. Launching a nuclear-capable bomber from an airfield shared with nuclear-armed US aircraft could raise one particular question mark in an adversary’s mind: is this a nuclear strike inbound?

The various platforms employed for long-range maritime strike are complementary, and each has strengths and weaknesses. The B-21 is aimed at the worst-case scenario and is not a replacement for the submarine’s stealthy, long-range, long-endurance, surgical capability. Nor would it generate the increased number of submarine personnel ^[14] critical for Australia’s transition to a force of operational SSNs.

An operational B-21 capability in the RAAF is well outside the timescales for any submarine capability gap. Indeed, there are likely to be a number of uncrewed alternatives in this timeframe.

The significant outlay would be better spent elsewhere. There are quicker and cheaper options for achieving an airborne, long-range maritime strike capability. As Hugh White has recently argued ^[15], introducing additional aircraft already in service would achieve a fully operational maritime strike capability much quicker and at a lower price and lower schedule risk than the B-21. I agree; aircraft such as the P-8 Poseidon ^[16] would be significantly cheaper to own and more flexible than the B-21.

In the same vein, building a follow-on Collins ^[17] would provide a sovereign, Australian-built option that would be best suited to fill any submarine capability gap. A fully operational capability could be achieved by the mid-2030s, at a lower price and with less risk. It would also provide an increase in Australia’s submarine capability that is essential for our defence, generate the personnel required for the transition to SSNs and provide greater flexibility and a larger range of options for the government, including anti-submarine warfare. Regardless of the claims of the B-21’s abilities ^[18], these are outcomes it cannot achieve.