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Regenerative shielding

The USS Prometheus

IKS Bortas shields hit

The port shields of a Vor'cha-class ship take a hit from a photon torpedo

Galaxy class deflector shield

The deflector shields of a Galaxy-class starship's stardrive section react to a tractor pulse

USS Enterprise-D fires on Duras sisters b-o-p

The forward shields of a D12-class Klingon Bird-of-Prey take a blast of phaser fire from the USS Enterprise-D

Trij's Bird-of-Prey

Class 5 Bird-of-Prey shields

Voyager shields

The deflector shields of an Intrepid-class starship's primary hull reacting to weapons fire

Constitution II class deflector status display

Deflector status display of a Constitution II-class starship

Graviton analysis

A graviton analysis of a Galaxy-class starship's shields

Deflector status display, Sovereign class

The deflector status display of a Sovereign-class starship

"Shields up, red alert!"
– Christopher Pike, 2258 (Star Trek)

Deflector shields or shield grids, generally referred to simply as shields, were a type of force field that surrounded a starship, space station, or planet that was used to protect against enemy attacks or natural hazards.


Deflector shields worked by forming a layer or layers of energetic distortion with a high concentration of gravitons around the object to be protected. The shield on starships was divided into six sections: forward, starboard, port, aft, dorsal, and ventral. (Star Trek Nemesis) Shield energies could be emitted by a localized antenna or "dish," such as a ship's navigational deflector, or by a network of "grid" emitters spread across the surface of an object, such as a starship's hull. Deflector shields have been standard equipment on starships since at least the 23rd century.

Normally, neither matter nor highly concentrated energy could penetrate a shield. Most matter or energy that came into contact with the shields was harmlessly deflected away when they were "up," or energized at a high level. This was significant in starship combat because shields were required for hull protection. Only minor hull damage would be expected during combat with the shields up. Without deflector shields, weapons in the 23rd and 24th centuries were capable of causing catastrophic damage to starship hulls almost instantly. (Star Trek II: The Wrath of Khan; Star Trek VI: The Undiscovered Country; Star Trek Generations)

Continuous or extremely powerful energy discharges could gradually erode a shield's integrity to the point of failure. Shield capacities varied depending on a variety of factors, ranging from available power to environmental concerns, making definitive and universal calculations of how much damage they could withstand difficult to estimate. As a result, tactical officers would constantly report on shield strength during combat, usually as a percentage of total effectiveness, with 100% indicating that the shields were fully operational and lower percentage scores indicating weaker shield conditions.

Specific sections of the shield grid could sustain more damage than others and be reinforced with additional power reserves, so tactical officers would report on the shields' health by section if necessary. Shields were said to be "holding" if the damage was insufficient to allow a compromise; if the shields were "buckling" or "failing," total shield protection was on the way. (Star Trek VI: The Undiscovered Country)

Shields used a frequency range to allow certain types of energy and matter to pass through or to increase the effectiveness of blocking them. Shield frequencies were rarely discernible without inspecting the controls on board the ship deploying them, making it difficult to tune weapons to the exact frequency of an opponent's shields in order to bypass them. (DS9: "The Jem'Hadar"; Star Trek Generations)

Starships would match their own shield and weapon frequencies in combat so that their shielding did not interfere with their own weapons. Some weapons technologies, including those commonly used by the Borg, had rapidly adjustable frequencies, allowing them to quickly penetrate a static frequency shield. To minimize the effectiveness of the weapon's retuned frequencies, an effective counter was to repeatedly and randomly alter the shield harmonics, though this tactic amounted to little more than a stall against the Borg. (Star Trek Generations; TNG: "The Best of Both Worlds")

A deflector shield took some time to activate. When taking a shuttlecraft on board via its tractor beam, a Constitution II-class starship needed exactly 13.5 seconds to lower and raise its shields, though this included the time required to tractor in the shuttle during an automated docking procedure; flying the shuttle in manually reduced this time significantly. (Star Trek V: The Final Frontier)

Shields on a Nova-class starship could be fully recharged after 45 seconds of charging the shield emitters. The shields were required to be lowered for this task. (VOY: "Equinox")

Normally, transporters were not capable of penetrating shields. (TOS: "Arena", "A Taste of Armageddon") Twenty-third century Federation starships, such as the Constitution-class USS Enterprise, could not transport through their own shields, but later starships such as the Intrepid-class vessels could transport personnel and objects freely to and from without having to lower their shields. (VOY: "Tsunkatse")

Federation starships typically used at least two different shield configurations. One type created an ellipsoid shield bubble that encircled the ship and a relatively large region directly adjacent to it. The other shield configuration employed a contour-conforming shield layer that extended a few meters beyond the main hull.

The ellipsoid shield configuration isn't shown until the 24th century. Though shield harmonics can be adjusted to change the shape of shields of the 24th century, it is unclear if ships could produce both shield configurations.

Some starships had a shield system advanced enough to allow protection of only specific areas of the ship, leaving other areas unprotected. This was useful in times when power reserves are low. Lowering portions of the shields would allow the use of transporters without completely sacrificing the protection that shields provide. This was also useful if a captain wanted to leave a section of the ship unshielded, like a cargo bay. (VOY: "Equinox, Part II")

Shields could be "extended" to encompass another vessel which couldn't use its own shields. (TNG: "The Next Phase") This could also be used on ships with weaker shields, by matching the ships' shield emitter frequencies. (TOS: "Mudd's Women"; TNG: "The Defector", "Deja Q"; VOY: "Equinox") While the extended shielding could provide some protection in the event of a shield failure on one ship, this technique put a strain on that ship's systems, and the overall strength of the extended shields was generally not as strong as two independent shield systems.


Shield strengths seemed to vary, making an exact calculation of how much damage they could take impossible. However, there were some examples:


USS Odyssey's shields penetrated

The USS Odyssey's shields penetrated

During the first battle with the Dominion in 2370, the USS Odyssey's shields were useless against the attacking Jem'Hadar fighters phased polaron beams, therefore the ship suffered significant hull damage during the attack, even losing viability to its port nacelle. To compensate the Odyssey's Captain Keogh attempted to alter the shield harmonics to compensate, but was unable to find an effective frequency, even after they had run through the full spectrum. Consequently, with the loss of their primary defensive mechanism, Keogh had engineering divert shield power to weapons to bolster their offensive capabilities. (DS9: "The Jem'Hadar") Four years later, Weyoun 5 was surprised to learn that Deep Space 9's shields held against the Dominions initial assault during the second Battle of Deep Space 9. In fact, he called such a feat "impossible", adding, "Federation shields have always proven useless against our weapons." Nevertheless, he was reassured by Gul Dukat that "I've found it wise to never underestimate the Federation's technical skill or Captain Sisko's resourcefulness." (DS9: "Call to Arms")

Solar flares can also damage shields and render them useless.

In 2266, Commander Sulu was forced to take the Enterprise out of the Minara System when the star entered its nova phase releasing a solar flare and trapping Kirk, Bones, and Spock on the planets surface. (TOS: "The Empath")

In 2364, Lieutenant, j.g. Geordi La Forge told Captain Jean-Luc Picard that the solar flare activity on a star the USS Enterprise-D was studying was increasing. The shields were weakened by the flare activity, but managed to hold. (TNG: "Symbiosis")

During a battle in the Klingon Civil War, Kurn destroyed two pursuing Birds-of-Prey by triggering a solar flare. (TNG: "Redemption II") During the Dominion War, Worf used this same tactic to destroy Monac Shipyards. (DS9: "Shadows and Symbols")

In 2373, Lieutenant B'Elanna Torres listed a solar flare as one of many factors that could interfere with USS Voyager's attempt to bring the Barzan wormhole to them with verterons. (VOY: "False Profits")

In 3189, the planet Reilling VII deployed shields to protect itself from solar flares. That year, it requested additional shielding from Federation Headquarters, which promptly sent a ship to assist them. (DIS: "Scavengers")


Hunter deflector shield

The handheld variation used by the Hunters

In 2369, Starfleet made first contact with a species from the Gamma Quadrant known as the Hunters. The first contact ended in a shootout on the Deep Space 9 Promenade, wherein the Hunters used a handheld deflector shield, integrated into their uniforms on their left arms. These shields collected the phaser fire and bundled it, letting the Hunters take several phaser shots without being hit. (DS9: "Captive Pursuit")

The script for "Captive Pursuit" refers to this technology as "optical deflector shields". [1]

Later that year, Major Kira Nerys and Lieutenant Jadzia Dax re-calibrated the inner deflector shield subsystems of Deep Space 9. (DS9: "Duet")

On Nepenthe, the house of William T. Riker and Deanna Troi had been equipped with deflector shields and scanners by 2399, as Riker said they had been having "a little trouble... with the Kzinti." (PIC: "Nepenthe")

In 3189, as the USS Discovery descended to the surface of a planet, Acting Captain Saru ordered Lieutenant Joann Owosekun to activate the deflector shields in bursts so as to cushion their landing. (DIS: "Far From Home")

Shield types[]

See also[]