Mr Putin knows that America's proposed anti-missile system would be too small to block Russia's still powerful missile armoury.

ECONOMIST: Anti-missile defence

The US and other regional allies fear North Korea is working to develop a nuclear warhead small enough to arm a missile, though it is not believed to have achieved this yet.

BBC: China criticises US missile defence plans

Shadows are now being armed with a small, still-classified guided missile.

ECONOMIST: Cheap smart weapons

Regional neighbours and the US fear Pyongyang is working to build a nuclear warhead small enough to put on a missile, but believe it does not yet have the capabilities to do so.

BBC: South Korea warns North on armistice threat

But a nuclear warhead would have to be small enough to fit onto, say, a Nodong missile - and it would have to be capable of withstanding the buffeting and other forces exerted on it during flight.

BBC: North Korea nuclear test raises uranium concerns

The crater was extremely small, but eyewitnesses said they had seen both a plane and a missile.

ECONOMIST: On the very eve, Baghdadis were still optimistic

Aegis began as a sea-based defense against hostile aircraft, but over three decades has evolved to become the most versatile missile-defense system in the world, due in no small part to the fact that destroyers and cruisers hosting the system can get wherever they need to be quickly.

FORBES: Can U.S. Defenses Cope With North Korea's Missiles?

And there will be thousands of small vendors flogging pink and orange neon cases for Apple iPhones, powered laptop backpacks, and USB missile launchers.

FORBES: Parasitic Vendors May Kill Trade Show

The most determined effort to develop a small, cheap guided weapon, though, is the Forward Firing Miniature Munition (F2M2, or Spike missile), from the Naval Air Weapons Station in China Lake, California.

ECONOMIST: Cheap smart weapons