Nuclear submarines will transform the capability of the Royal Australian Navy. Each has several times the combat effectiveness of the Collins-class diesel submarines we now have.
Submarines propelled by nuclear reactors can spend much more time on station to threaten the enemy. They have vastly greater mobility, constrain an adversary's operations over much wider areas and are more likely to launch successful attacks.
This is why the government said on Thursday that it would acquire such boats, with help from the US and Britain.
The RAN's need for nuclear submarines has always been obvious: diesel submarines are simply inefficient when deployed as far as our navy sends them, to waters well beyond Indonesia.
Now the threat from China has forced the government to accept the challenges that have formerly deterred us: public dislike of anything nuclear, and the daunting difficulty of safely operating a technology with which we have almost no experience.
We will do this only with much help from our friends.
Australia's current submarines are driven by electric motors fed by batteries that are periodically recharged by diesel engines. The French submarines we formerly expected to buy would have been the same.
A nuclear submarine has a small reactor that produces steam to drive a turbine engine, like those in power stations. The reactor has enough fuel inside it to run for many years, maybe the whole life of the boat.
This frees the nuclear submarine from the two big limits on diesel submarines: the need to refuel and, above all, the need to occasionally stick an air pipe above the water to run diesels. The pipe, called a snort, may be detected, so a crew wants to extend it as little as possible. The whole point of a submarine is to not be seen.
Avoiding detection constrains a diesel submarine as it's making the long passage between its base and its zone of operations.
The faster it goes, the faster it depletes its batteries and is forced to extend the snort and fire up its diesels for a recharge. So an Australian diesel submarine might move at only eight knots (15 km/h) as it covers a journey of maybe 6000 kilometres from its base near Perth to, say, the middle of the South China Sea.
Depending on exactly where it's going, the trip will take two to three weeks. Since it also has to spend that much time getting back to base and may have enough food and other supplies for only eight weeks at sea, it will spend only about three weeks on station.
The nuclear submarine, unworried about fuel consumption and not needing to snort, may move at least twice as fast during the passage and therefore might spend six weeks on station.
This alone makes the nuclear submarine about twice as useful, an advantage that increases when its navy wants to send it even farther from home.
Once in the operations zone, near the enemy, the diesel submarine crew is even less willing to recharge. Enemy ships and aircraft are more likely to be encountered; their radars could see the snort. Radar satellites are likely to be focused on the operations zone.
So the diesel boat will typically move at only two to three knots when it's on station, hardly using any energy.
The seriousness of this problem is underlined by how diesel submarines are designed: their engines and batteries have to be as large as possible so the boats can stay fully submerged for as long as possible between very quick recharges.
A nuclear submarine on station faces no risk of a snort being detected, and its speed can again be much higher, restricted only by the need not to make too much noise or, in shallow water, cause a noticeable wave on the surface. It can quickly shift position, so it effectively threatens a vastly larger area.
For example, a navy might know that an enemy submarine is somewhere near a port, so ships using that port require heavy protection. But if the submarine is nuclear-powered, the navy must consider that in only 10 hours that boat could be causing mayhem 400 kilometres away. Operations over a vast swathe of ocean are threatened.
Preparing for a torpedo attack will often require a submarine to move quickly, to place itself in the path of its unsuspecting target. A diesel submarine can accelerate to do this, running down its batteries. But a nuclear submarine can easily move even faster, so it can lunge at targets that are farther away.
Having made its attack, and knowing the enemy will seek retribution, the nuclear submarine can rapidly steam away.
The Falklands War of 1982 illustrates the colossal capability of underwater nuclear energy. As Argentinian troops landed on the islands, the Royal Navy, forewarned, already had nuclear submarines charging down the Atlantic Ocean at full reactor power.
They were doing 29 knots (54 km/h), at least three times the speed that an Australian diesel submarine might use if it wanted to maintain a useful period on station when it finally arrived.
Once they were near the Falklands, the British submarines moved at high speed to make intercepts. One, HMS Conqueror, sank the old Argentinian cruiser Belgrano. After that, the Argentinian navy mostly stayed in port.
The main advantage of a diesel submarine is that, when it's running batteries, it's quieter than a nuke, and can therefore go into riskier places. The advantage is not so great that the US, Britain and France are willing to operate submarines of both types, however; they all have only nuclear boats.
- Bradley Perrett was based in Beijing as a journalist from 2004 to 2020.
- This article is supported by the Judith Neilson Institute for Journalism and Ideas.