The U.S. Navy tested a hyper velocity projectile in Hawaiian waters last summer. A report from USNI News says the destroyer USS Dewey fired 20 of the experimental rounds from the barrel of its deck gun during the RIMPAC naval exercises.
Just last month, Chinese social media published murky pictures of a ship putting to sea carrying what appeared to be a railgun. A flurry of reports followed about an electromagnetic wonder weapon able to fire rounds a hundred miles at seven times the speed of sound. According to reports, the Pentagon’s railgun project has struggled with technical problems and if China has been able to test its railgun at sea, it would appear to be way ahead.
Then Sam LaGrone of USNI News reported that the U.S. tested an alternative system last summer, less capable, maybe, but much cheaper and available much sooner. The Hypervelocity Projectile, the HVP, was developed for the American railgun, but as progress stalled, the Navy decided to marry its futuristic projectile with a launching system it already had – the venerable 5-inch gun that sits on the deck of many U.S. warships.

If it works, high tech bullets from barrels built for the age of gunpowder could be operational years before any railgun. With built-in guidance systems, a range of forty miles and velocity more than three times the speed of sound, the HVP would have several roles, none more important than as part of a layered defense against the Navy’s nightmare – a swarm of incoming missiles.
Experiments are also underway to fit the HVP to the 155 millimeter cannon used by the Army and the Marines.