"Two key limitations that Navy surface ships currently have in defending themselves against ASCMs and ASBMs are limited depth of magazine and unfavorable cost exchange ratios. Limited depth of magazine refers to the fact that Navy surface ships can use surface-to-air missiles(SAMs) and their Close-in Weapon System (CIWS) Gatling guns to shoot down only a certain number of enemy unmanned aerial vehicles (UAVs) and anti-ship missiles before running out ofSAMs and CIWS ammunition—a situation (sometimes called “going Winchester”), that can require a ship to withdraw from battle, spend time traveling to a safe reloading location (which can be hundreds of miles away), and then spend more time traveling back to the battle area.

Unfavorable cost exchange ratios refer to the fact that a SAM used to shoot down a UAV or anti ship missile can cost the Navy more (perhaps much more) to procure than it cost the adversary to build or acquire the UAV or anti-ship missile. In the FY2018 defense budget, procurement costs for Navy SAMs range from about $976,000 per missile to several million dollars per missile, depending on the type.

In combat scenarios against an adversary with a limited number of UAVs and anti-ship missiles, an unfavorable cost exchange ratio can be acceptable because it saves the lives of Navy sailors and prevents very expensive damage to Navy ships. But in combat scenarios (or an ongoing military capabilities competition) against a country such as China that has many UAVs and anti ship missiles and a capacity for building or acquiring many more, an unfavorable cost exchange ratio can become a very expensive—and potentially unaffordable—approach to defending Navy surface ships against UAVs and anti-ship missiles, particularly in a context of constraints on U.S.defense spending and competing demands for finite U.S. defense funds.SSLs, EMRG, and HVP offer a potential for dramatically improving depth of magazine and the cost exchange ratio:

Depth of magazine: SSLs are electrically powered, drawing their power fromthe ship’s overall electrical supply, and can be fired over and over, indefinitely, aslong as the SSL continues to work and the ship has fuel to generate electricity.The EMRG’s projectile and the HVP (which are one and the same—see nextsection) can be stored by the hundreds in a Navy surface ship’s weaponmagazine.

Cost exchange ratio: An SSL can be fired for a marginal cost of less than one dollar per shot (which is the cost of the fuel needed to generate the electricity used in the shot), while the EMRG’s projectile/HVP has an estimated unit procurement cost of about $25,000"