What are nuclear-powered submarines and how do they work? Australia’s firepower ambitions explained

With Australia making a deal with the United States and the United Kingdom to begin a nuclear-powered submarine program, we can expect the Aussie subs will look a lot like the latest versions in the US and British arsenals.

The fleets of the US Navy and Royal Navy have two kinds of submarines – categorized as attack and ballistic missile. Both are powered by nuclear reactors, which convert water into high-pressure steam that turns turbines to propel the subs.

But attack subs and ballistic missiles subs – often called “boomers” – serve very different purposes. Australia is signing up for the nuclear-powered option, or attack sub, rather than the boomers, which are nuclear-armed, with nuclear warheads on their ballistic missiles.

Here’s the difference between the two:

Attack submarines

Canberra wants attack subs – the jack-of-all-trades backbones of the US and UK sub fleets.

Dolphins love subs. USS John Warner commander Dan Caldwell said that when subs are cruising along the surface, dolphins are swimming along with them 90% of the time. Here a dolphin swims in front of the USS John Warner, during its sea trials in May. Submariners actually wear medals on their uniforms that have dolphins on them — maybe that's why the dolphins are so fond of the subs.

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“Attack submarines are designed to seek and destroy enemy submarines and surface ships; project power ashore with Tomahawk cruise missiles and Special Operation Forces (SOF); carry out Intelligence, Surveillance and Reconnaissance (ISR) missions; support battle group operations; and engage in mine warfare,” the US Navy says atop its attack submarine fact sheet.

The US has three classes of attack subs in its fleet of 53. The newest of these are the 19 of what’s called Virginia class.

Armed with dozens of Tomahawk cruise missiles and torpedoes, the 377-foot, 8,000-ton Virginia-class subs can cruise at more than 28 mph (46 kph) and stay submergedindefinitely. Their time underwater is limited only by the need to resupply provisions for the crew of 132.

During a tour of the Virginia-class USS John Warner in 2015, CNN secured a look inside.

The sub doesn’t even have a periscope. Rather it uses a photonics mast – a piece of electronic wizardry that includes high-definition and infrared video – to monitor the battlespace. The information is displayed on large screens in the command center, with a joystick controlling the whole show.

The USS Indiana, a nuclear-powered attack submarinedeparts Port Canaveral in Florida on October 1, 2018.

The UK’s four Astute-class attack subs are even faster than the US subs, capable of more than 35 mph (56 kph) submerged, and like the US carry the Tomahawk cruise missile.

“Tomahawk IV is the latest version of the missile. It has a longer range than its predecessors (well in excess of 1,000 miles), can be directed at a new target in mid-flight, and can also beam back images of the battlefield to its mother submarine,” the Royal Navy’s website says.

That’s the kind of firepower and endurance Australia wants as it looks to protect its northern waters from any naval threats and project its naval power into the South China Sea, where it, along with the United States, looks to blunt Chinese influence and protect freedom of navigation.

An Astute-class submarine operated by the UK's Royal Navy, heading down the Firth of Clyde, in September 2020.

Ballistic missile submarines

The UK and US boomers carry Trident ballistic missiles armed with multiple nuclear warheads. Their mission, essentially, is to stay at sea for months at a time, the vast majority of it submerged, and be prepared to launch a retaliatory nuclear strike should an adversary launch one of their own against the UK or US.

The ballistic-missile submarine USS Pennsylvania returns home to its Washington state homeport following a strategic deterrence patrol in 2015.

Ballistic missile subs are quiet beneath the waves and extremely hard to detect. They are the linchpin of deterrence, assuring that an adversary of the US or UK would pay a horrific price for a first-strike nuclear attack.

Each of the US ballistic missile subs can carry 20 Trident missiles (16 for the UK subs) with as many as eight warheads (three for the UK subs) per missile. They are able to be shot over a range of 4,600 miles (7,400 kilometers). The nuclear warheads have blast yields between 100 kilotons and 475 kilotons. By contrast, the atomic bomb dropped on Hiroshima, Japan, during World War II had a yield of 15 kilotons.

The US has 14 ballistic missiles subs, while Britain has four. These are not the submarines Australia is signing on for.

When will Australia put subs to sea?

It takes a long time – possibly decades – to develop a nuclear-powered submarine and get it deployed. The three-party deal announced Wednesday only provides for an 18-month study to see how to best build nuclear-powered subs for Australia.

Australian Prime Minister Scott Morrison said it could be 2040 before the new subs are in the Australian fleet.

President Joe Biden delivers remarks about a national security initiative on September 15, 2021 in the East Room of the White House in Washington, DC. President Biden is joined virtually by Prime Minister Scott Morrison of Australia and Prime Minister Boris Johnson of the United Kingdom (Photo by Oliver Contreras/Sipa USA)

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Thomas Shugart, a former US Navy submarine commander who is now a fellow at the Center for a New American Security, said with the security situation in the Indo-Pacific, Australia may be hoping its subs can be in the water sooner.

“There will be a number of tradeoffs that will need to be considered that could affect the timeline – local content versus using established suppliers, a new design with more advanced characteristics versus existing US/UK submarine or propulsion plant designs, etc.,” Shugart said.

“Given the eroding military balance in the Indo-Pacific, I’d hope that 2040 is a no-later-than sort of date. At the same time I have a hard time imagining a deployment timeline of less than about a decade, even moving with the speed of urgency and using much existing design and suppliers.”