Because they are unstoppable by current defence systems, they are leading towards a destabilising arms race between the main developers - the United States, Russia and China.

Australia's interest in hypersonics has been more in the area of hypersonic aircraft design. One day, hypersonic aircraft might carry passengers long distances in a short time - perhaps a few hours from Sydney to London. Australia has also taken part in tests of the weapons technology with the US at Woomera.

What then are hypersonic weapons, and why do they matter?

"Hypersonic" means they can travel at more than 1.7 kilometres per second - that is Sydney to Melbourne in eight minutes, but some hypersonic missiles will be much faster than that, and could cover the distance in under two minutes.

Hypersonic missiles come in two variants. Hypersonic cruise missiles, or HCMs, are launched from platforms such as aircraft and ships and are powered by rockets or jets throughout their flight. Unpowered hypersonic boost-glide vehicles, or HGVs, are launched into the upper atmosphere on ballistic missiles, which then release them to zoom into their targets at low level at speeds of up to Mach 27. (The claimed speed for the Russian Avangard HGV.)

Hypersonic weapons could be fitted with either conventional or nuclear warheads, but even in conventional form they are very effective against hard targets because of the enormous kinetic energy generated by their very high impact speed.

Russian President Vladimir Putin, who was angered by the US walking away from the Intermediate-Range Nuclear Forces Treaty, claims to have three hypersonic weapon systems tested and close to deployment.

The US is working towards having operational hypersonic systems in place by October 2022. Images have already been released of the AGM-183A Advanced Rapid Response Weapon (ARRW) launched from USAF aircraft and reportedly capable of reaching speeds of Mach 20.

The main concern with these weapons is that they could be used with little warning to disable an adversary's nuclear or conventional strike capability.

The Avangard HGV is, according to Russian officials, capable of sharp high-speed horizontal and vertical movements in flight which means that it is "absolutely invulnerable" to any defensive system. The manoeuvrability of these systems also makes it harder for the target nation to determine the intended targets.

Major naval platforms, including American carriers, have no defence against these weapons.

Hypersonic weapons could also be used to deliver a decapitating strike against a country's leadership.

To exploit what it sees as an American vulnerability, China has flight-tested shorter-range hypersonic missiles as a key element in its strategy to dominate East Asia. Its DF-17 HGV is said to be capable of reaching US bases in Guam from China. The DF-17 is expected to be deployed by next year and could be the first hypersonic weapon to enter operational service.

France and India have active hypersonics development programs, and both are working independently with Russia, according to the US Rand Corporation.

Japan aims to have a hypersonic weapon ready for testing by 2025, presumably with the North Korean nuclear missile threat in mind.

Meanwhile, the US is also working towards having a network of sensors in low-earth orbit that would track incoming hypersonic missiles - but intercepting them would not be possible with current technology.

There have of course been many past arms races to gain an advantage with "game-changing" weapon systems - heavy machineguns, jet fighter aircraft and nuclear weapons come to mind.

But the strategic advantages gained by revolutionary new systems are usually short lived - potential enemies always catch up, and then it becomes a matter of who can deploy the most to deter other parties from using them.