So-called "hypersonic missiles" are raising tensions in North-east Asia following tests, first by China last August and then two more by North Korea, the most recent just last month.

Publications including The New York Times, The National Interest and Asia Times have called hypersonic missiles a "game changer", as have US senators Lindsey Graham and Angus King. America's top general Mark Milley said the Chinese hypersonic test last year was "very close" to "a Sputnik moment", referring to a Cold War episode in which Americans suddenly feared they had fallen dangerously behind the Soviets in aerospace technology.