Defense screens are an integral part of any interstellar starship, as they provide protection for both a ship and its crew (or, as left, even droids and other equipment) from dangerous environmental conditions ranging from ionizing radiation, natural energy discharges, physical collisions, as well as weapons fire. Although the tactical usefulness of shields is often quite obvious, they more often serve a role of simply controlling the immediate environment of a starship and keeping it within acceptable limits. The Imperial paradigm of shield technology revolves around the operation of two separate and independent forms of protection, particle shields (also known as concussion shielding) and ray shields (sometimes referred to as energy shielding). Both types of shielding are necessary to fully protect a starship, and are often found on all military vessels.

Particle shielding is as necessary to interstellar ship operation as hyperdrive engines. Without the protection that this kind of shielding provides, collisions with interstellar meteoroids during a hyperjump or impacts with other spacecraft or debris at high sublight speeds could shred or destroy a space-cruiser. Although capable of aptly dealing with micrometeoroids, the weak particle shields of this TIE fighter (right) were overwhelmed by collision with a comparatively large asteroid. Because they are designed to forcefully retard or deflect high-velocity projectiles, particle shields can also drastically reduce the destructive effects of various missile weapons and explosives. But by the same token, they must be dropped in order to launch starfighters or missile weapons. Normally these kind of procedures only leave the vessel unprotected for several microseconds, making the temporary drop a difficult window to exploit. However, as handy as concussion shielding is for deflecting micrometeoroids, space-junk, and blunting the occasional missile impact, they generally provide no significant protection against nonsolid materials, with the exception of being able to partially scatter and blunt ion cannon bolts. But when faced with much less dense ionized gasses found in some nebulae or the free-floating superheated plasma found in turbolasers, their performance drops to ineffectual levels; such protection is the arena of the ray shield.

Protection against nonsolid artillery such as lasers and turbolasers are the responsibility of the second shielding system, ray shielding. Ray shielding is a much more energy-intensive affair than particle shielding and as such these shields are only raised during situations where their protection is expressly necessary. They must be properly angled during battle situations in order to provide maximum protection against an onslaught from non-concussion weaponry, as their powers to absorb, reflect, or disperse energies from nonsolid weapons (left) explicitly depends on properly calculated trigonometry. A ray shield that is not properly angled to protect against a ray weapon approaching on a certain vector can "miss" the bolt entirely, providing no impediment and allowing it to directly strike the hull. These occurrences are rare, however, as Imperial computer technicians and shield operators spend years in training to learn how to effectively operate the complex deflection mechanisms necessary to protect ships like Imperial Star Destroyers. A talented shield deflection officer is one of the most prized assets to an Imperial commander, as they can significantly increase the durability and effectiveness of a vessel's defense screens.

Since ray shielding is only useful in combat situations, its use is somewhat restricted. Individuals must apply for permits to own and operate such shielding and show just cause to have it, although fear of space pirates is usually enough of a reason. As touched on earlier, particle shields are designed to protect a ship from kinetic impacts (right); collisions with small asteroids, space debris, or even other vessels. These kind of shields are generally quite durable, but their generators must be kept very close to the surface of a vessel in order to properly operate. This makes them prone to disablement by concentrated fighter or bomber strafing. When they do operate, they greatly increase the durability of the ships they protect, destroying all manner of small space debris and increasing the outer hull's tensile strength.

Particle shields achieve this effect by producing a polar molecular dispersion/reinforcement field which permeates several millimeters into the hull. As the name implies, the protective energy-sheath has two distinct properties, each of which dominate a different pole of the field. The inward-pole, or interior pole has the effect of increasing the molecular bond dissociation energy (in other words, it strengthens the covalent bonds) of the atoms that compose the hull of the ship it is protecting. This increases the outer hull integrity of the ship. The outward-pole, or exterior pole, has the opposite effect, however; it drastically decreases the molecular bond dissociation energy of incoming matter, often causing it to explosively shatter into free-floating atoms.

Particle shielding fields can, however, be cancelled out by interaction with other particle shields, making it possible for some vessels to "latch" onto others (left) while avoiding catastrophic damage. In the case of unshielded or lightly shielded missiles and other explosives, the exterior pole of a ship's particle shield can often cause premature detonation of the warhead. In this case much of the explosive energy (which would have otherwise been released after the missile had pierced the armor, embedded itself deep inside of the ship, and then exploded) instead impacts against the outer hull, on armor that has increased molecular durability thanks to the interior pole of the field. Although it does not protect entirely against the effects of the explosion, the end result is often little more than cosmetic surface scorches or moderate damage to the outer armor, rather than catastrophic internal damage or loss of atmosphere.

Ray shields, however, operate in an entirely different manner. Instead of operating with exotic molecular dispersion fields, they are specifically designed to counteract the effects of the complex electromagnetic jacket that guides and contains turbolaser bolts. These systems are meant to reflect, splinter, or otherwise defeat these confinement beams and keep the superheated plasma that they channel away from the hull. Dampening the electromagnetic field that guides the beams is ordinarily not enough; this would result in an effect somewhat similar to a flak burst, but would occur so close to the vessel that a great deal of damage could still be imparted to the hull. Despite the protective molecular reinforcement provided by the particle shields, ray shields only operate in this way when no other alternative, save letting the bolt strike the hull directly, is possible.

In a best-case scenario, a ray shield will reflect a bolt entirely by effectively "bouncing" the confinement beam away from the ship and shunting the plasma along another vector and into open space. The shield achieves this through the use of a series of carefully angled and controlled ultrathin electrostatic repulsion fields. Given that the fields are perfectly angled and the weapon being deflected is not too powerful, a ray shield can toss away fire without taxing its energy reserves. But the heavier a bolt is, the stronger a confinement tube is required to hold it, and in some cases the ray shields are not strong enough or angled correctly to effectively turn an offending confinement beam away.

In such a case, a second alternative comes into play. If a shield is not powerful enough (or not angled exactly) to bounce a bolt along a harmless trajectory, the shield may actually compensate by splintering the confinement beam into a series of smaller and more manageable sub-tubes (left). In such a scenario, however, reflecting the splinter bolts back into open space is impossible, because by the time the ray has splintered, the offending energy has already begun to disperse across the shield and there is no one angle that will deflect every sub-bolt. All the ray shield system is capable of doing now is doing it's best to shunt the sub-tubes to other deflector fields in the grid, trying to split them into even smaller fractions and absorb the energy into its capacitors. The ray shield capacitors are designed to quickly dissipate the heat buildup, and this causes and allow the shields to "regenerate." This ability is not infinite, however; when the amount of energy-per-second stressing the ray shields exceeds the amount of energy-per-second it is capable of dissipating, the capacitors soon overload and the shield falls.

In a worst case scenario, save letting the bolt strike the hull directly, a ray shield will not be able to effectively reflect or even splinter the confinement beams of an incoming bolt. In such a scenario, the system will default to dampening the electromagnetic jacket around the bolt entirely. This will have the effect of causing the bolt to "flak," which will decrease the amount of damage dealt to the defending vessel by a significant degree. But given that the ray shields of a ship can not extend beyond a few centimeters from the hull without demanding exorbitant costs in energy, the flak burst ends up behaving more like an explosion (right) and still can cause serious damage to the outer hull. Although this is preferable to being struck by an intact bolt, it is still a highly undesirable contingency.

Shortly after first contact with the United Federation of Planets, several alterations were made to Imperial standard shield procedure, and indeed the operation of shield technology altogether. The two most significant changes were spearheaded by Grand Admiral Sher Khal'Saad and various leading scientists of the Imperial Science Directorate. The first involved the integration of ray and particle shielding, such that particle shields could not be dropped during a battle situation in order to save energy reserves for weapons or extra ray shield capacity. This practice, increasingly common among Imperial commanders in recent years, proved to give Imperial cruisers a distinctive disadvantage when they came up against unexpected ion cannon or missile weaponry. Ray shields do not effectively deflect the bolts of ion cannons, because ion cannon weaponry lacks an electromagnetic containment beam. Although the electrostatic planes of the ray shields do have some interaction with the charged particles of an incoming ion bolt, the fields are simply not strong enough to deflect a full on bludgeoning from a condensed packet of high energy ions. Particle shields, on the other hand, can provide some protection against ion bolts, but only at high energy levels. A significant strike from an ion bolt while particle shields are down entirely can be catastrophic.

In the case of launching missiles or other weapons, particle shields can be "cold dropped," that is, disengaged by simply interrupting the power flow to their subsystems for a short amount of time. This allows physical objects to be launched, but leaves an extremely weak low-power "residual" field in place. Although the weak residual field is of no defensive value, when the shields are re-engaged it allows them to "skip" back up very quickly to their original levels without having to generate a field from scratch. Effectively, the shield can be instantaneously turned off and on at will, so long as it's not turned off for more than a full second.

But in the case of battles such as the embarrassment at Hoth, Imperial commanders disengaged their particle shields entirely in order to divert more energy to their weapons and ray shielding systems. When the unexpected ion bolts began to fly from the defiant Rebel base, the star destroyers in orbit found themselves with no defenses against the onslaught, and were unable to instantaneously re-engage their particle shields because they had been off for too long. By the time they could get the particle shields back up, the Rebel dissidents had already escaped.

The second change to shield technology was much more technically oriented. Because of the peculiar phased nature of StarFleet armaments, the shields of Sher Khal'Saad's defense fleet could not properly defend against many of the exotic weapons used against them. As such, photon and quantum torpedoes as well as phasers were able to pass effortlessly through the uncalibrated shields of the star destroyers and significantly damage their hulls. As it turns out, the shields were not entirely useless in the battle, but would require extensive alteration in order to perform effectively in any future confrontations with the Federation.

It cost Imperial Intelligence a pricy sum from the Ferengi Alliance in order to obtain the technical information that enabled Imperial scientists to overcome this setback, but within a year of contact with the Federation, a solution to the "phase problem" was found. Imperial ray and particle shielding systems were outfitted at Kuat Drive Yards with a special piece of Alpha Quadrant technology called a phase discriminator, which allowed the shield systems to properly counteract the exotic phasic properties of StarFleet weaponry. When Imperial and Federation forces clashed once again a year later, the shields did their job well.