What Is A Cloaking Device On Star Trek And How Does It Work?

Welcome to Trekspertise, a series where we break down the technology, history, details, and decisions that make the Star Trek universe so complex — and so fun.

Cloaking devices were first introduced on "Star Trek" in the original series episode "Balance of Terror," showing that Romulan vessels could somehow make their ships appear invisible. Not only did they vanish on the Enterprise's sensors, but they also appeared to physically vanish on a ship's viewscreen. The cloaking device was a perfect dramatic conceit for a species that was written to be kind of insidious and dastardly (read our history of the Romulans here on /Film). Starfleet didn't have cloaking devices, and thus had no means of subverting Romulan technology. Romulan cloaking devices became a central plot point of the original series episode "The Enterprise Incident," wherein Kirk (William Shatner) was tasked with sneaking onto a Romulan vessel in disguise and stealing a cloaking device so that Starfleet could study it. 

Cloaking devices have been a regular feature on "Star Trek," then, since the very beginning. It was a tactical advantage enjoyed not only by the Romulans, but the Klingons as well. Because the Federation is a peacekeeping organization devoted to diplomacy and scientific study, they had banned cloaking devices on their own vessels thanks to the Treaty of Algeron. Said treaty was signed in the year 2311, about 20 years after the events of "Star Trek VI: The Undiscovered Country," but 50 years before the events of "Star Trek: The Next Generation." Cloaking devices are used by villains, not heroes. 

Of course, many in the Federation have felt that cloaking devices should be installed on Starfleet vessels, and some villainous admirals (like Terry O'Quinn's Admiral Pressman in the "TNG" episode "The Pegasus") feel that Starfleet is at a disadvantage without them. 

Admiral Pressman would be happy to learn about the USS Defiant on "Star Trek: Deep Space Nine," which seems to have been given special permission to use a cloaking device. It appears that the Federation does have access to the technology, but the mechanics and installation are far from common knowledge. One can assume that Starfleet security keeps the secrets of cloaking devices under strict lock and key. 

Because it's such a secret, the actual technical ins-and-outs of cloaking devices aren't discussed often on any of the "Star Trek" shows. According to "The Enterprise Incident," a cloaking device is tied into a ship's shields and is able to, through light-redirecting means, "bend" light around it, making it appear invisible. The device does something similar to sensor signals. If a cloaked vessel were to go to warp, however, it could be detected immediately, as all ships leave a warp signature behind them. A cloaking device cannot mask that, because cloaking devices are literally just a trick of the light. 

Also, because a cloak is tied to a ship's shields, a vessel cannot have its shields up for the few seconds it is turning invisible. If an attacking vessel were to smack a photon torpedo into a cloaked vessel by chance, right when it was cloaking, it would do the maximum amount of damage. As stated in "Star Trek VI: The Undiscovered Country," Klingon vessels also cannot fire any weapons while cloaked, making cloaking devices better suited for stealth than for combat. Of course, in "Country," the Klingons had developed a vessel that could fire while cloaked, which proved to be an existential threat to the Federation. 

And no, cloaked vessels cannot "see" each other if they are both cloaked.

It's long been assumed that Romulans invented cloaking devices and that Klingons acquired the tech in some sort of trade, but that's only been confirmed in non-canon novels. Canonically, no one knows who invented the first cloaking technologies. 

Naturally, many episodes of "Star Trek" are devoted to beating cloaking devices. One might have seen the "Star Trek: Enterprise" episode "Minefield," wherein the crew of the Enterprise found a way to detect cloaked mines in deep space. Also, it seems that looking closely at a place where a cloaked vessel is located will reveal that there is a slight "gravitational microlensing" at play. No cloak is perfect. In the "Star Trek: The Next Generation" episode "Unification Part II," it was revealed that Starfleet vessels could set up specialized, multi-ship sensor grids — like a massive dreamcatcher in space — that could detect any cloaked vessels that tried to move through them. 

As seen in the "Next Generation" episodes "The Next Phase" and "The Pegasus," some ships had even begun combining cloaking technology with a type of interphasic technology that could make the particles in a whole starship insubstantial to other physical matter. This would have allowed a ship to sail right into a planet, passing through matter like a ghost. 

In both those episodes, though, it was stated that interphase tech was unstable and accidents were way too common. In "Phase," Geordi (LeVar Burton) and Ensign Ro (Michelle Forbes) were exposed to a phase explosion, and became like ghosts on the Enterprise. They could see each other, but could also move through walls. In "Pegasus," the titular ship fired up a phase cloak but rematerialized in an asteroid, killing most everyone on board. Maybe phasing technology isn't such a great idea.