Last week, President Vladimir Putin of Russia announced the deployment of the Avangard among the first in a new class of missiles capable of reaching hypersonic velocity - something no missile can currently achieve, aside from an intercontinental ballistic missile during re-entry.

Such weapons have long been an object of desire by Russian, Chinese and American military leaders, for obvious reasons: Launched from any of these countries, they could reach any other within minutes. No existing defences, in the United States or elsewhere, can intercept a missile that can move so fast while manoeuvring unpredictably.