The U.S. Navy Quietly Tested Mach 3 Heavy Gun Shells That Could Revolutionize Surface Warfare

The new shells fire from a standard Navy gun and can down flying targets much more cheaply than missiles.

U.S. Navy Gunnery Exercise
U.S. Navy photo by Senior Chief Petty Officer Matt Bodenner

The U.S. Navy, without fanfare or notice, tested a new weapon last summer that could revolutionize surface warfare. The hyper velocity projectile (HVP) is a Mach 3 shell fired from existing guns on cruisers and destroyers. A guided projectile, HVP can drop high explosives on enemies on the ground up to three times as far as conventional ship gun ammo with a high rate of precision. It can also intercept incoming anti-ship missiles, providing an economical alternative to increasingly expensive anti-missile interceptors.

, the guided missile destroyer USS Dewey fired 20 new HVP projectiles during the 2018 Rim of the Pacific (RIMPAC) exercises. Although the test was unclassified, it was not reported at the time by the U.S. Navy. It was the first known use of HVPs at sea by a warship.

Large surface combatants in the U.S. Navy all carry the (127mm) Naval Gun System. Unlike railguns, these are chemical energy guns that use gunpowder to launch projectiles, a basic technology hundreds of years old. Guided missile cruisers of the Ticonderoga-class carry two Mk.45 guns, while guided missile destroyers of the Arleigh Burke-class carry one. These guns are typically used for shore bombardment, softening up enemy defenses before an amphibious assault, although in a pinch they could be unleashed against enemy surface ships and incoming aerial threats.

The unguided nature of these rounds, however, makes them less accurate than missiles. Amphibious assaults are also extremely rare, making the guns increasingly difficult to justify in the age of fast-moving missiles.

In the early 2010s, the U.S. Navy and BAE Systems began work on railgun hyper velocity projectile technology. Railgun HVPs would travel at a speed of up to Mach 7, necessitating special projectiles to withstand the rigors of hypersonic flight. In a “why not?” moment, HVP technology was ported over to Mk.45 gun shells. After all, the Navy had scores of conventional five-inch guns in daily use, while it has zero operational railguns.

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HVP projectile mockup.
BAE Systems

The result is a HVP shell that reaches Mach 3 and at 40 miles has a range three times greater than conventional shells. The shell also incorporates fins and a guidance system, allowing it to engage pinpoint targets on land or missiles and aircraft in the air. It can also do so substantially cheaper: USNI News the cost of the shell should be about $100,000 at the very most. That’s expensive for a gun shell, but cheap compared to the $2 million dollar price tag of a surface-to-air missile.

Suddenly the old gun system, once the outlier of a ship’s armament package, is near the center again. If the Navy HVP shell proves good at intercepting enemy missiles, the Mk.45 could become a key defensive weapon against incoming missile and aircraft swarms. Relying on it for that purpose could even free up precious slots in a warship’s vertical launch silos for anti-ship missiles. It looks like the Navy has taught an old dog some new, important tricks.

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