A ballistic missile can travel at hypersonic speed. A cruise missile can be slower than sound. A hypersonic glide vehicle needs a rocket to get moving, but it is not powered throughout its glide. The labels overlap because they describe different aspects of flight.
Start with propulsion and trajectory, then ask about speed. That order reveals more than a headline announcing a new maximum Mach number.
Ballistic describes the flight path
A ballistic missile gains most of its initial speed from rocket propulsion. After the powered boost, much of its journey follows a path shaped primarily by gravity. Depending on its range and design, that journey may take it outside the atmosphere before its payload returns toward Earth.
Ballistic does not mean that every part of the flight is unguided or that every weapon follows an identical arc. Guidance, maneuvering and the behavior of the re-entry vehicle differ between designs. The basic label tells readers about the dominant flight pattern, not every control feature.
Nor does it give a single speed. A missile accelerates, coasts and encounters changing conditions during flight. A quoted maximum may describe one phase, rather than the speed maintained throughout the journey.
Cruise missiles remain powered
A cruise missile uses aerodynamic lift and remains powered through most of its atmospheric flight. That makes it more aircraft-like in this respect than a weapon traveling principally on a ballistic trajectory.
Cruise is not a synonym for slow. Different designs fly at subsonic, supersonic or hypersonic speeds. Their propulsion, flight altitude, navigation and intended role vary. A general description of the category should not be mistaken for a specification sheet for every member of it.
This distinction also explains why range alone makes a poor comparison. Two weapons credited with similar ranges may spend their journeys in very different flight conditions. Their launch platforms, payloads and operating assumptions may also differ.
Hypersonic is both a speed term and a policy label
In aerodynamics, hypersonic commonly describes speeds above Mach 5. Contemporary weapons discussions usually mean something more specific: systems designed to maneuver through the atmosphere at hypersonic speeds.
Two principal forms appear in that narrower discussion. A hypersonic glide vehicle is accelerated by a rocket, then separates and glides through the atmosphere. A hypersonic cruise missile uses air-breathing propulsion during sustained flight after its initial acceleration.
Many conventional ballistic missiles also exceed Mach 5. That does not automatically place them in the same category as the newer maneuvering systems discussed in defense programs. The U.S. Government Accountability Office's hypersonic-weapons report explains its own definition and exclusions. Those boundaries reflect the report's purpose, rather than a rule that changes the meaning of speed.
When two sources seem to disagree, check whether one is describing a flow regime and the other a procurement or policy category. Both may be using the term consistently within different definitions.
Mach is a ratio, not one fixed speed
Mach number compares an object's speed with the local speed of sound. The NASA Glenn explanation notes that the speed of sound depends on the gas and its temperature. Atmospheric temperature changes with altitude, so a Mach value does not translate into one universal number of kilometers per hour.
That is why a speed conversion needs stated conditions. It is also why comparing two advertised Mach numbers without knowing where they apply may suggest a precision the underlying claims do not provide.
One weapon can carry several labels
Launch platform, range and flight behavior are separate ways of describing a weapon. Air-launched tells you where the journey starts. Cruise tells you something about powered flight. A range classification addresses distance under the definition being used. Several such labels can correctly apply to the same system.
The category also does not establish the payload. A discussion of trajectory or propulsion should not be read as evidence of a particular warhead. Claims about an individual weapon need a source for that variant, rather than an assumption drawn from another member of the same broad family.
Speed does not establish invulnerability
An interception problem involves the weapon's trajectory and maneuvering, warning time, sensors, command systems and the defenses available. Speed matters, but it is one part of that problem. Layered air defense brings several of those functions together.
A test announcement raises another set of questions. Was a complete weapon tested? Which flight conditions were demonstrated? Was the system a prototype, a production item or an operational deployment? An announced capability and a fielded capability are different milestones, just as an approved sale is different from a delivery.
For the next missile headline, keep four questions in view: how is it powered, what path does it follow, where does the quoted speed apply, and what has actually been demonstrated? Those answers make the label useful.