Currently the US and Russia are developing Anti Ballistic Missile (ABM) systems that can reliably intercept a
ballistic missile at Mach 18. I believe Russia's latest A-XXX series is already operational around Moscow, and the US is developing the NGI in addition to THAAD and PAC-3.
India is also developing an ABM system but it is not yet operational; Shaheen-III constantly changes its trajectory in the final stage to make it extremely difficult for an ABM to predict its path and intercept it. Iranian missiles use
MARV, where the warhead can slightly change its direction till impact.
Ababeel follows a ballistic trajectory, but carries 3-8 warheads at once, so even if some of them are intercepted you will still potentially have a nuke slip through.
Defeating a missile is not just about speed, it's detection and tracking that counts as well.
Hypersonic glide vehicles and
Hypersonic Cruise Missiles are deadly in this regard as they hide from long range radars behind the earth's curvature, so by the time they are detected they're too close and fast to intercept. Their movement is also unpredictable (they can change direction somewhat like a fighter jet), making it near impossible to plot an interception path.
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