Hypersonic munitions have become a baseline requirement for major militaries. The United States, for example, plans to procure at least 10,000 of Castelion’s Blackbeard hypersonic missiles over the next three years, while Russia, Iran, and Pakistan have all claimed that they used “hypersonic” missiles in recent conflicts.
However, the term ‘hypersonic’ is loaded and vague when left unqualified. If left to the most basic standard, it could refer to a munition that flies faster than Mach 5, which, in turn, places very different types of munitions under one label and treats them equally.
In practice, however, most ‘hypersonic’ adoption currently leans on rocket boosters, in ballistic missiles, or glide vehicles such as the Blackbeard. Arguably, however, the gold standard for hypersonics is the air-breathing cruising missile, which uses a ramjet or a scramjet to stay under power at hypersonic speed.
Measured against that standard, complete hypersonic adoption arguably remains more elusive for most militaries, including the US, which has yet to field its own air-breathing Hypersonic Attack Cruise Missile. Yet, interestingly, the countries leading in terms of the air-breathing hypersonic stack is Asia’s leading power, China – with India rapidly closing in with its own indigenous technologies and solutions.
Defining a ‘Hypersonic Missile’
Air-Breathing Hypersonic Cruise Missiles
The US Congressional Budget Office (CBO) defines a hypersonic missile as “a missile that travels within the atmosphere (rather than above it) at speeds greater than Mach 5 and that can maneuver in the atmosphere for much of its flight.”
Thus, a ballistic missile that passes Mach 5 on descent, or manoeuvres only within its terminal phase, falls outside that definition. Prior to the Russia-Ukraine War, most had framed and anticipated that hypersonic missiles would be air-breathing systems.
Indeed, the US had tested a demonstrator as early as 2013 through the X-51 Waverider, which had reached Mach 5.1 using a scramjet propulsion system. Back then, the US Air Force (USAF) called the demonstration flight “the longest air-breathing hypersonic flight ever.” Not long after, Russia promoted its 3M22 Zircon as a scramjet-powered missile – but more recent findings show that the Zircon might also involve ballistic missiles.
The value of air-breathing missiles generally – be it hypersonic, supersonic, or subsonic – is survivability. For example, earlier generation subsonic cruise missiles introduced the use of sea-skimming in maritime environments, and later land-attack solutions provided terrain-hugging. The basic objective of flying low is to operate under the adversary’s air defence coverages, at least their long-range, high-altitude coverages.
So, for example, terrain-hugging cruise missiles can leverage the nap-of-the-earth to exploit gaps in the adversary’s air defence coverages. Subsonic cruise missiles can leverage these types of low-altitude flight maneuvers most effectively, but supersonic- and hypersonic-cruise missiles can draw on these advantages to an extent, requiring trade-offs in terms of turn radius, reaction time, atmospheric drag, and thermal stress compared to subsonic. That said, supersonic- and hypersonic-cruise missiles can still leverage these far better than most ballistic missile-based solutions.
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