- "You can't fight what you can't see."
- ―Urai Fen
While sensor jammers could leave a starship invisible to sensors, cloaking devices generated cloaking fields that completely absorbed all incoming sensor scans while shielding the host ship's emissions and reflected energy, thus rendering the starship invisible to both sensors and the naked eye. A single cloaking device unit towered over the average Human with a balloon-shaped computer core standing over a series of cloaking field antennas. Below lay the power cells, which were connected to the cloaking field matrix by a series of wires.
The only sensor capable of sensing a "cloaked" vessel was the expensive and rare Crystal gravfield trap, which tracked the gravitational fluctuations created by a large mass in space. Thus, any cloaked vessel was unable to hide from the CGT. However, such cloaking shields also came at a disadvantage to their users because they drained a large amount of energy from the starship's power plant, and (though dependent on the size of the device) a single unit cost millions of credits.
The hibridium model cloaking device's worst drawback was perhaps the "double-blind" nature of the cloaking shield, which also blocked the host ship's scanners and communication systems. Crews and passengers on cloaked ships were unable to peer beyond the cloak's shroud. Since visual navigation was impossible, any other form of navigation could only be exercised by preprogramming astrogation routes. The vessel was thus effectively isolated from the rest of the galaxy. Communications, combat operations, and sensor sweeps could only occur when the cloaking field was lowered or disabled. The cloaking device did nothing to impair senses dependent on the Force, however, and trained Force users could detect even cloaked ships in battle with ease.
Another drawback common to both was that a cloaked ship could be tracked was by the ship's magnetic signature. This tactic, used mostly by Separatist commander Admiral Trench, allowed tracking torpedoes to be fired and follow the ship even if it was cloaked.
Cloaking devices were once fairly common, based on stygium crystals mined on the planet Aeten II in the Dreighton Nebula. However, as the crystal supply dwindled, cloaking devices followed suit, until there were none left at all.
Before the rise of the Galactic Empire, cloaking devices were virtually unknown, but not unheard of. Around 32 BBY, Sienar Design Systems developed and built a cloaking field generator for Darth Maul's Scimitar, powered by stygium crystals. Jango Fett also had one, which had been added onto Slave I by Mentis Qinx, a dockyard owner on Tatooine, in 22 BBY. The Imperial Handbook: A Commander's Guide stated that any ship found with a cloaking device installed should be captured intact if at all possible.
During the Clone Wars, Jedi General Anakin Skywalker piloted a Stealth ship with a powerful cloaking device through the Blockade of Christophsis commanded by Admiral Trench. Anakin was able to utilize the stealth ship against Trench by using Trench's own tracking torpedoes against him. Thus the ship helped to break the blockade surrounding Christophsis for the time being.
Later in the Clone Wars, the fleet of CIS Admiral Pors Tonith utilized cloaking devices in its ships, including the flagship Corpulentus. These ships used the device to their advantage during the Battle of Praesitlyn.
Emperor Palpatine's personal Lambda-class T-4a shuttle was also rumored to be equipped with a stygium cloak. By the time of the Battle of Yavin, Aeten II's reserve of accessible crystals had been depleted, making the manufacture of new stygium-based cloaks a virtual impossibility.
Grand Admiral Martio Batch managed to create a cloak based on hibridium obtained from Garos IV, but it was inefficient and suffered from double blindness—occupants of a starship using one could no more see the rest of the galaxy than the rest of the galaxy could see them. This double blindness limited its military effectiveness.
Batch sent the Tarkin to Aeten II, where it blew up the planet, exposing thousands of previously unreachable stygium crystals for Batch to use. He recreated the old stygium technology and applied it to the Phantom TIE project, but Rebel saboteurs completely destroyed the project, including an Executor-class Star Dreadnought equipped with a stygium cloaking device that housed the project, the Terror, and Batch was forced to flee.
Several weeks before the Battle of Endor, a Rebel task force led by Rogue Squadron destroyed a cloaking device project to be implemented on an Executor-class Star Dreadnought at Fondor. Wedge Antilles, piloting a captured TIE Hunter, flew into the vessel's trenches and destroyed the three cloaking relays. The resulting explosion not only destroyed the Star Dreadnought, but also the Imperial shipyard in which she was housed.
Palpatine also commissioned a second team to work on the Vorknkx Project, aiming to make improvements to the hibridium cloak under the supervision of Grand Admiral Zaarin. After Zaarin attempted to overthrow the Emperor, control of the Vorknkx Project passed to Grand Admiral Thrawn. The team successfully equipped the CR90 corvette Vorknkx with a hibridium cloak but were unable to overcome a problem which made the device unstable when entering hyperspace.
Knowing that Zaarin was obsessed with obtaining the best technology, Thrawn allowed him to capture the Vorknkx, which was destroyed when Zaarin attempted to flee into hyperspace while cloaked.
During the chaotic years of the Galactic Civil War, the gangster-turned-warlord Tyber Zann would utilize a fleet of frigates and destroyers, as well as F9-TZ Transports, equipped with some form of cloaking device. He and his lieutenant Urai Fen were also equipped with their own personal cloaking devices.
The original hibridium cloak prototype found its way to the Emperor's storehouse on Wayland, where it remained hidden until the return of Grand Admiral Thrawn. Thrawn used the technology in a number of creative ways, including hiding a shipload of TIE/LN starfighters and mole miners as "empty cargo" in the Battle of Sluis Van; using cloaked asteroids as a unique siege engine at Coruscant; and carefully lining up ships above and below a planetary shield (with the ones beneath the shield cloaked) so fire from the orbiting ships would appear to pass right through the shield. This tactic led to the conquest and occupation of several New Republic member worlds including Sluis Van and Ukio without the heavy damage to lives, industry, and resources sustained during most conventional planetary invasions.
After Thrawn's death, innovation in finding a use for the device focused on the Computerized Combat Predictor. Ten years later, the Predictor still performed insufficiently to warrant further hope.
The Empire Reborn used a shuttle that was equipped with a one-way cloaking device. In 14 ABY, Jedi Knight Jaden Korr went to Yalara on a mission of destroying the planet's cloaking device, to prevent the Imperial Remnant from laying hands on it.
However, the clone Grodin Tierce, who had been created with some of Thrawn's own thought processes, found a new use for the cloaking device, hiding three Star Destroyers in the outskirts of the Bothawui system, guiding them in by use of a comet that barely grazed the cloaking field.
Behind the scenes
In Star Wars: Battlefront II, the Bothan Spies for the Rebels have an ability called Stealth. This is a one way cloaking shield. The one way part may be due to game mechanics. The Knights of the Old Republic games also featured stealth-generating belts rendering the user invisible.