ISS Enterprise caught in a Tholian Web while cloaked
A Tholian drydock containment web
The USS Enterprise encased in a Tholian web
In the Star Fleet Universe, certain Tholian ships are capable of 'casting' web at long range - as seen here against the Seltorians, who prove the most bitter of foes for the Tholian race.
The Tholian web is an energy net that is "spun" by Tholian spacecraft around an immobilized enemy vessel. The more vessels that are used to generate the web, the faster it is deployed. A web can be disrupted by destroying the ships creating the web before they finish. (TOS: "The Tholian Web"; ENT: "In a Mirror, Darkly", "In a Mirror, Darkly, Part II")
The web is composed of a series of energy filaments which are generated in a web pattern around a target vessel. Once these filaments have been sealed, the web becomes self-generating and the web-spinning crafts no longer need to maintain the web. If any craft within the web attempts to leave, they may be shredded by the energy filaments. Weapons fire, such as photonic torpedoes, are also destroyed by the web and the resulting detonation energy is dispered across the energy filaments. (ENT: "In a Mirror, Darkly")
The Tholian web can also be used as a high power immobilization field/tractor beam to pull captured starships back to Tholian territory. (TOS: "The Tholian Web")
The Tholians in the mirror universe are capable of creating webs. In 2155, the ISS Enterprise (NX-01) was destroyed while caught in a Tholian web. Several escape pods from the Enterprise were also destroyed as they attempted to traverse the web, although some were able to leave through the gaps. (ENT: "In a Mirror, Darkly") The Tholians proceeded to form another web over their docking portal to prevent surviving Enterprise personnel from escaping aboard the USS Defiant; however the Defiant destroyed the Tholian ships and escaped. (ENT: "In a Mirror, Darkly, Part II")
In 2268, the USS Enterprise was nearly trapped inside of such a web while on a mission to rescue Captain Kirk from spatial interphase. The Federation starship narrowly escaped being dragged back to a Tholian port as they were able to leave the web before it was complete. (TOS: "The Tholian Web")
- The effects for the Tholian web in The Original Series was created by Mike Minor.
Apocrypha
The Tholian web is a staple part of the tactical combat wargames of the Star Fleet Universe, such as Federation Commander (where full rules for web will be formally published in the upcoming Tholian Attack module) and Star Fleet Battles.
In the SFU, there are two prominent types of devices that can produce webs - the Web Generators (attached to 'Archaeo' Tholian ships - such as the Patrol Corvette, the SFU reference for the ships seen in the Original Series) which allow a ship to 'spin' web, and the more powerful Web Caster (usually seen on larger 'Neo' Tholian ships - designs unique to the SFU) which can project web at long range, or produce a concentrated web 'fist' capable of acting as a direct-fire weapon.
In the SFU setting, the Tholians arose in M81, where they eventually established a galaxy-wide empire - in which the use of web was key to their ability to suppress opposition. Indeed, the Seltorian race (a species of insectoids granted 'most-trusted-race' status within the Tholian Will) only managed to overthrow their masters once they discovered the Web Breaker - a weapon uniquely capable of disrupting the web. When the Tholian remnants who fled to the Milky Way established their Holdfast, web was once again the key to their survival in the face of hostile neighbours (such as the Klingons).