A cloaking device, also known as a stealth device, was a type of technology that could render a starship invisible.
Darth Maul engages the Scimitar's cloaking device over Tatooine
A cloaking device rendered an object completely invisible to nearly all forms of detection, by disrupting the electronic signature its various systems and sensors normally emitted. The object, however, could still be tracked via its magnetic signature. A form of experimental starship technology, cloaking devices allowed ships to bypass enemy vessels and fleets undetected, rendering them essentially invisible to ordinary scanners. However, an interdiction field rendered stealth technology inoperable, and vulnerable to detection. Cloaking devices could be powered by either hibridium or stygium crystals.
A practical cloaking device had been a dream of Chiss Defense Force scientists for generations.
The Scimitar cloaking
Darth Maul's Scimitar had a cloaking device, which he used to launch a sneak attack on pirates assaulting Trade Federation forces over Kellux. Taken by surprise, the pirates were destroyed by proton torpedoes and mines deployed by the Scimitar.
Prior to the Clone Wars, Admiral Trench engaged cruisers equipped with cloaking devices. However, he was able to use tracking torpedoes to hit them whether they were cloaked or not.
The cloaked stealth ship
During the Clone Wars, Republic engineers utilized experimental starship technology to create the stealth ship, a heavily-armed vessel fitted with a cloaking device. Jedi General Anakin Skywalker used the craft to deliver supplies to Senator Bail Organa's camp on Christophsis. However, Skywalker also used it to attack Trench's command ship, the Invincible. Despite the failure of his first attack, Skywalker used Trench's tracking torpedoes against him, leading the missiles back to the Invincible, destroying the bridge, severely injuring Trench, and briefly breaking the blockade.
Later in the war, the bounty hunter Cad Bane was given a modified Rogue-class Porax-38 starfighter with a cloaking device, as payment from his Sith Lord client, Darth Sidious. Sidious himself utilized the cloaking device aboard the Scimitar, Darth Maul's former vessel, to reach Dathomir undetected. There, he and General Grievous engaged Maul and his Shadow Collective in battle, a final confrontation with Mother Talzin. Asajj Ventress used the cloaking device aboard the Lancer-class pursuit craft Banshee to deliver Anakin Skywalker and Obi-Wan Kenobi aboard a Providence-class Dreadnought to rescue Quinlan Vos.
A G-1A starfighter equipped with a cloaking device.
Grand Moff Wilhuff Tarkin's personal corvette, the Carrion Spike, had a cloaking device based on the stealth ship used at Christophsis, and was powered by stygium crystals. During the Galactic Civil War, it was very rare for small ships such as the Millennium Falcon to have cloaking devices. Cloaking devices were used by shadow troopers during battles against the Rebel Alliance.