(BBC): The UK, US, and Australia will begin co-operating on research into hypersonic weapons and how to defend against them, the government has said.
The programme will be part of the AUKUS partnership, a security pact announced by the three countries last year.
It follows the development of hypersonic missiles by China and Russia and their purported use by Russia in Ukraine last month.
Hypersonic weapons are those that exceed five times the speed of sound.
They are harder to defend against because of their speed as well as the fact they fly at low altitudes – beyond the line of sight of ground-based radars – and can manoeuvre mid-flight.
The UK does not currently possess hypersonic missiles.
The US and Australia have an existing joint programme to develop the weapons but the UK government stressed the focus of the new venture would be on defence.
It said there were no plans for the UK to develop its own hypersonic weapons but the new programme would help it assess whether it would need to develop them in future.
It added the latest announcement was not related to Russia’s use of the weapons in Ukraine but said the fact other nations were investing in them meant the UK had to think about how to defend against them.
On 19 March, Russia claimed to have used a hypersonic missile to destroy an arms depot in western Ukraine, and US military intelligence has suggested Russian forces have used them repeatedly since.
The attacks would mark the first use of hypersonic missiles in combat.
It came just months after China caught US intelligence by surprise when it tested two nuclear-capable hypersonic missiles.
Each circled the globe in low-orbit space before coming back down to Earth, the second missing its target by only about 24 miles (40 km).
The missile is thought to combine a so-called fractional orbital bombardment system, which sends missiles into a partial orbit of the Earth to strike from an unexpected direction, with a hypersonic glider, which remains in the outer atmosphere and is hard to detect until later into its flight.
The tests demonstrated China had far more advanced space capability than had previously been understood.
North Korea has also claimed to be in the process of testing hypersonic missiles.