Why nuclear submarines?
Nuclear submarines are powered by nuclear reactors which produce heat that creates high-pressured steam to spin turbines and power the boat’s propeller.
They can run for about 20 years before needing to refuel, meaning food supplies are the only limit on time at sea.
The boats are also very quiet, making it harder for enemies to detect them and can travel at top speed – about 40kmh – for longer than diesel-powered subs.
The first nuclear submarines were put to sea by the United States in the 1950s. They are now also in use by Russia, France, the United Kingdom, China, and India.
A senior US defence official told reporters in Washington DC: ‘This will give Australia the capability for their submarines to basically deploy for a longer period, they’re quieter, they’re much more capable.
‘They will allow us to sustain and to improve deterrence across the Indo-Pacific.’
Zack Cooper, a senior fellow with the American Enterprise Institute, said nuclear submarines would hugely boost Australia’s military capability.
‘They are going to be much, much more capable in the large, expansive ocean that is Australia has to deal with,’ he told the ABC.
Will Australia have nuclear weapons?
Scott Morrison made it clear that the nuclear-power submarines will not have nuclear missiles on board.
Australia has never produced nuclear weapons and signed the Treaty on the Non-Proliferation of Nuclear Weapons in 1973 which prevents non-nuclear states which don’t already have them from developing nuclear weapons.
Mr Morrison also said the Australia has no plans to build nuclear power stations which are widely used around the world.
‘But let me be clear, Australia is not seeking to acquire nuclear weapons or establish a civil nuclear capability,’ he said.
‘And we will continue to meet all our nuclear non-proliferation obligations.’
Are they safe?
The nuclear reactors are shielded from the rest of the submarine in a separate section to protect the crew from dangerous radiation.
The US has an excellent safety record with its nuclear-powered fleet although early Russian subs suffered a few accidents which caused 20 servicemen to die from radiation exposure between 1960 and 1985.
At the end of their 20-year lifetimes, the contaminated parts of nuclear reactors need to be disposed deep underground in special waste storage cells.
Anti-nuclear campaigners say any leaks of radioactive waste could lead to an environmental disaster.
Greens leader Adam Bandt called the submarines ‘floating Chernobyls’ in reference to the 1986 nuclear power plant explosion in the Soviet Union.
Australia needs to replace its six ageing Collins-class submarines.
In 2016 it signed a deal with French Company Naval Group to build 12 diesel-electric attack subs – but the parties were in dispute over the amount of building that would be done in Australia.
That deal has now been torn up in favour of nuclear powered subs aided by the US and UK who will provide the technology to Australia.
The West is becoming increasingly concerned about the growing assertiveness of China in the Indo-Pacific region where it has made huge territorial claims in the South and East China seas, clashed with Indian troops and repeatedly flown planes over Taiwan.
Mr Morrison wants Australia to have serious defence capability to deter China from encroaching in the Pacific and long-range nuclear submarines are just the ticket.
China has vastly built up its military in the past few years and now possesses six Shang-class nuclear powered attack submarines, equipped with torpedoes and cruise missiles.