Cruise missiles that are difficult to detect, increasingly fast and capable of carrying nuclear warheads are spreading, especially in Asia, complicating arms control and raising the risk of catastrophic conflict.

Until recently, most concerns have focused on the actual or potential spread of nuclear-tipped ballistic missiles in China, North Korea, India and Pakistan — the four Asian states known to have atomic arms. Ballistic missiles, launched by rocket engines, follow an arc-like trajectory, attaining hypersonic speeds on the downward leg of their guided journey towards a target.

Until now and probably for some time yet, all long-range ballistic missiles, with atomic warheads small enough to fit on them, are deployed exclusively for strategic nuclear deterrence. The five official nuclear weapon states — United States, Russia, China, Britain and France — use their long-range ballistic missiles, whether launched from land, air or sea, to deter possible attacks by other nuclear-armed nations.