Electromagnetic Rail Gun ProposalRail guns have long been seen as a "Holy Grail" of naval weapons, as the technology promises hypersonic launch velocities without the use of conventional propellants. Instead of propellants, the output of the ship's power plant may be shunted into a large capacitive device, storing high levels of energy, which are released short bursts as the gun fires. Alternatively, a grouping of compensated pulsed alternators capable of delivering a momentary high spike of energy may be used. The latter approach appears to have the advantages of smaller footprints, inherent graceful degradation should one or more alternators fail, and lower total system weight.

A Rail Gun operates by making use of the Lorentz force created on a moving armature. The gun consists of two parallel rails electrically connected via an armature which holds the projectile. Current from the power source is sent down one rail, across the armature, and then down through the other rail back to the power source. This current flow creates a magnetic field around the armature, generating a propulsive force which slides it down the rails.

With large currents, railguns have the ability to produce great accelerations and thus high muzzle velocities, without the hazards of chemical explosive charges used in conventional guns. This reduces the vulnerability of the ship to damage, as there are no magazines, only shell rooms, and the shells themselves may not contain a burster. The hypersonic velocities generated give the projectiles large kinetic energies, long range, and short flight times.

BAE Systems won a contract to deliver a 32 megajoule lab launcher in June 2007 to the Office of Naval Research (ONR) Electromagnetic Launch Facility, located in Virginia at the Naval Surface Warfare Center's Dahlgren Division Laboratory. On 31 January 2008, test firing began with this launcher. The railgun was fired at 10.64MJ (megajoules) and the 7 lbs. (3.2 kg) test slug projectile attained a muzzle velocity of 8,268 fps (2,520 mps). A newer launcher is now under construction that will allow multiple shots and energies approaching 30MJ.

This weapon has fallen out of favor in the USN, with funding reduced for fiscal year 2021 budget request to $9.5 million, down from around $15 million requested in fiscal year 2020 and roughly $28 million in fiscal year 2019. This level of funding may move the railgun into the "promising, but not recommended for further development" category in the near future.

However, the Hypervelocity Projectile (HVP) originally developed as part of the railgun program is now seen as being useful for conventional naval guns and has seen its funding greatly increased. See 5"/62 (12.7 cm) Mark 45 for details.