Hypersonic glide vehicle. A hypersonic glide vehicle (HGV) is a type of warhead for ballistic missiles that can maneuver and glide at hypersonic speed. It is used in conjunction with ballistic missiles to significantly change their trajectories after launch.  Conventional ballistic missiles follow a predictable ballistic trajectory and are vulnerable to interception by the latest anti-ballistic missile (ABM) systems. The in-flight maneuverability of HGVs makes them unpredictable, allowing them to effectively evade air defenses. , hypersonic glide vehicles are the subject of an arms race.

Projects 

 DF-ZF (developed and deployed) / Mach 5–10
 GDF-600 (concept) In addition to a unified payload the Guangdong Aerodynamic Research Academy claims to be exploring fitting the conceptual weapon with various submunitions including what it calls a patrol projectile.
 DF-27 (developed and deployed) / >Mach 8.6

 VERAS (program launched in 1965 and cancelled in 1971)
 VMaX (first flight test took place on June 26, 2023 from the DGA's site in Biscarrosse and was successful)
 VMaX-2 (under development; first flight test expected in 2024 or 2025)

 HGV-202F (under development)
 LRAShM (testing phase)

 Fattah-2 Mach 13-15

 Hyper Velocity Gliding Projectile (HVGP) (under development)

 Hwasong-8.
 Hwasong-12B (not tested yet). It is possible that the Hwasong-12B was renamed from Hwasong-8.
 Hwasong-16B (tested in April 2024).
There have also been reports of other hypersonic glide vehicle being mounted on the other ballistic missiles.

 The Avangard (developed and deployed) / Mach 27-28

 Hypersonic Technology Vehicle 2 (experimental)
 AGM-183 Air-launched Rapid Response Weapon (ARRW) (under development)
 OpFires (under development)
 Common-Hypersonic Glide Body (C-HGB) (in development for US Army (LRHW) and US Navy Conventional Prompt Strike (CPS))

Countermeasures 
Boost-glide weapons are generally designed to avoid existing missile defense systems, either by continually maneuvering or by flying at lower altitudes to reduce warning time. This generally makes such weapons easier to intercept using defensive systems intended for lower-altitude "low-tier" targets. Flying at lower speeds than short-range ballistic missile warheads makes them easier to attack. Those that approach with very low terminal attack profiles are even subject to attack by modern hypervelocity guns and railguns.

Hypersonics, like the Avangard HGV, generally use scramjet engines to achieve hypersonic speeds. Scramjet engines function only when the glide vehicle reaches mach 4.5. These engines are disengaged as the HGV enters the terminal phase of its flight. Failure to deactivate the engines would cause a catastrophic build up of heat in the vehicle as the atmosphere becomes denser during reentry, prematurely destroying the vehicle. Therefore, the terminal phase of an HGV's re-entry is similar to that of a multiple independently targetable reentry vehicle. For instance, the Avangard would not hit its target while "zig-zagging" at Mach 27, but rather would impact at a velocity under Mach 4 and on a linear trajectory. The superior evasion capabilities that HGVs employ are largely limited to the upper atmospheric flight span.

See also 
 Hypersonic flight
 Hypersonic weapon
 Maneuverable reentry vehicle
 Multiple independently targetable reentry vehicle
 Non-ballistic atmospheric entry

References

Hypersonic aircraft
Ballistic missiles