And by the way ... tunable and multiple wavelength output ...
A free electron laser is not only tunable - but with enough power - it can deliver multiple output wavelengths as harmonics of its tunable microwave resonance cavity. The desired weapons effect is therefore not to produce just one output frequency - but can be set to group multiple EM wavelengths to pump a solid to liquid, liquid to gas, and gas to plasma - simultaneously.
When dealing with meta-material cloaked projectiles - this ability to rapidly reset whole groups of EM output frequencies in response to observed target state changes allows the FEL / PHASER to penetrate metamaterial cloaks through plasma shock ablation.
Simply put, with a couple of nuclear reactors behind it, a FEL/PHASER is a Star Trek disintegrator beam with potential orbital reach - especially when provided with reverse conjugate acoustic gas-phase optics to correct for atmospheric scatter. By being able to ramp thru EM frequency ranges from radio to infrared to visual to X-ray, solid phase projectiles can be simply erased in flight with a sweep of the output beam.
This ability has special value for penetrating reinforced command and control bunkers. It would be considered a more humane penetrator than current penetrator warhead designs, since direct contact with the beam would disintegrate a human instantly. Note that secondary plasma shockwaves can be extremely damaging to surrounding human tissues and organs, with enough force to shatter bone, as well as 20 foot thick reinforced concrete walls.
A mobile sea-based platform is ideal for the same reasons ballistic missile submarines provide deterrence. Nothing in the FEL/PHASER specs prevent it from being submarine-based. or capable of producing EM wavelengths tuned to penetrate water to submarine operational depths, or from submarine depths to orbit. Torpedo defense is possible with sufficient FEL/PHASER power at radiowave frequencies.
Nominally, there are current space treaties preventing the use of nuclear power in near earth space for military purposes. While these treaties are honored, sea-faring FEL/PHASER systems will remain its principal mode of deployment.
We are not talking about deadly white sharks with lasers mounted on their heads.
We are talking about really, really, big sharks capable of running silent and running deep for months at a time with arrays of FEL/PHASERS installed into converted sea-launched ballistic missile silos. The big boomers will have a new mission protecting the fleet and near space.
Biting the hand that feeds IT
