On Stardate 1709.1 the Bonhomme Ri Romulan Space. Suddenly, it vanished from the sensors, reappeared directly in front of the outpost and fired what later came to be called a "plasma torpedo". The torpedo obliterated the outpost's deflector screens, nearly destroying it. A second shot finished the intruder's job. Then the ship simply disappeared from view.
That was the first encounter with the Romulans after almost a century since the battle of Cheron. The vessel that destroyed S-4023 (and also S-4024 and S-4025) was a Romulan P-1A Bird of Prey with a first generation cloaking device.
Later, a third generation cloaking device has been obtained by the U.S.S. Enterprise in an espionage mission.

The Klingons gained the technology from their alliance with the Romulans in exchange for their D-6 Raxor and D-7Klolode battle cruisers. Thus the three major powers in this part of the galaxy came to posses what proved to be one of the most formidable weapons ever.

Star Fleet, which used the cloaking device on its vessels in the late 2200's and early 2300's, has decided that the peaceful (mostly) mission definition of the Explorer type of starships precludes its use. Further- more, the overall shape and hull materials used in the Galaxy, Ambassador, and Oberth class starships would interfere with the cloaking device. Although it is still possible to cloak them, the energy necessary increases beyond reasonable limit. Today, only specialized scouting, stealth, and battle ships use cloaking devices.

The Klingon Empire has used the cloaking technology ever since their technology exchange with the Romulans in 2263, and continues to do so. Nearly all of its Bird of Prey type ships are equipped with it as are the D- 6, D-7, D-8 (K'T'Inga), and the new K'Vort class battle cruisers.

Our Empire naturally still uses the cloaking device. Although much about them is now unknown due to the fifty-year contact breach after the Tomad incident, it is certain that their newest vessels, the D'Deridex class warbirds, are equipped with a new generation of cloaking devices which have so far defied all Federation attempts at detection without the use of tachyons.

The Romulan cloaking device is an energy screen generator used to render a ship or object invisible to the eye and to most sensor systems. This is accomplished by gravitational lensing, the creation of a distorted image of an object when it's light is focused by gravity. In the case of a cloaking device, the light is focused so that the object's index of refraction (the phase velocity of radiation in free space divided by the phase velocity of the same radiation in a specified medium) matches its surroundings, making the object transparent. Cloaking a ship requires precisely balancing the radiative emissions from the warp drive nacelles, dissipating all electromagnetic radiation, gravitational fields and other energy emissions emanating from the ship, and distorting space in such a way that electromagnetic radiation and energy emissions are directed around the ship through subspace at velocities faster than light.

Cloaking devices have been classified into the following categories according to their overall effectiveness:

Mk 1 Cloak: Original usage, early Warbirds only. Used electromagnetic radiation shielding quite effectively to cloak only visible and near-visible radiation. Can instantaneously cloak and decloak, but required large amounts of power.

Mk 2 Cloak: A major improvement on the Mk 1, this device cloaked all electromagnetic radiation, except high energy Gamma rays. Can instantaneously cloak and decloak, but was remarkably inefficient. Craft: Romulan Scouts and Warbirds, also Klingon D-7 Cruisers, and later the joint Romulan/Klingon scout and Bird Of Prey.

Mk 3.0 Cloak: The first gravity distorting cloak. The early prototype craft had problems with energetic effects occurring inside the cloak as a result of trapped spurious thermal emissions within the cloaking field. This was overcome by giving the craft a green coloration. This tuned the thermal energy to a frequency where it could leak very slowly through the cloak without revealing the ships presence, still common practice on most cloaked vessels. This early Mk 3 had only the spherical field setting and could not be effectively wavemapped. It could not instantly cloak and decloak, but saw much use on most Romulan craft and the Bird Of Prey.

Mk 3.1 Cloak: This improved device featured instantaneous propagation of the spherical cloak, and first saw use of the wavemapped cloak. It is reported to have been used as above and as an upgraded cloak for D-7 Cruisers. A green coloration was still necessary.

Mk 3.2 Cloak: This version saw the creation of the fine tuned cloak, using the special dedicated computers. This device was perhaps first created by the Klingons, but required large power reserves. The Romulans later reworked the idea into a more efficient form (officially designated the Mark 3.2a). The old cloak is still in active service on older Klingon craft.

Mk 3.2a Cloak: Romulan reworking of the 3.2. No special coloration of the craft is necessary, although the nullifier cores require less energy when the ship has a green color. The cloak is still extensively used by Romulans and Klingons alike.

Mk 3.3 Cloak: This latest version allowed powering down of all non-finely tuned cloaks instantly. It is only fitted, as far as is known, to Romulan Warbirds. Klingons claim to still use the 3.2a.

Experimental Mk 4 Cloak: There is an experimental cloaking device which utilizes a highly-wavemapped, adaptive, asymmetrical dispersion pattern. This cloaking device's cloaking generator coils are equipped with field actuators that change the dispersion pattern, to be most efficient in any interstellar condition, considering many variables, such as gas density, electric and magnetic fields, and fluctuations in the subspace domain. These field actuators compensate for any of these variables or active scans if the vicinity of the cloaked ship is being probed. There is no danger of a spatial ripple occurring. This would render a ship undetectable, except with a tachyon heterodyne detection grids, which, if powerful enough, could detect a ship that was cloaked in this manner.

Romulan ships do not make use of matter/antimatter reactors like most vessels but instead of that they make use of an quantum singularity drive. The Quantum Singularity Reactor is one of the greatest Romulan achievements. Quantum singularity is the same what happens in a black hole. This so called artificial gravity well can generated a tremendous amount of energy which gives the ships their thrust. An quantum singularity reactor can only be shut down at a docking station due to the fact that it cannot be restarted in space. The reactor itself houses a singularity: a point in space where the laws of physics supposedly break down. What happens here is that matter is continuously fed into the singularity. The gravity from the singularity pulls the matter together, forcing it to not only fuse, but to bump into each other, etc. This causes an enormous amount of energy to be obtained, and we never have to worry about fuel: it is all around us. It is not only more efficient then matter/antimatter drive but also much more powerful. One of the problems that Federation scientists have had with artificial singularity reactors is that they simply cannot see how the ship can move with this massive gravitational anomaly within the heart of the ship. The solution, although the Federation is too egotistical to realize it is that the Romulans use the same thing that they do to control gravity: they place a Inertial Dampening Field around the reactor. This way, they trick the ship into thinking the reactor isn't even there at all. This way, their ships are even lighter than Federation ships, allowing them to move faster and respond more quickly to external stimuli. Indeed, this process releases the equivalent of a standard Federation Matter/Antimatter Reaction Assembly.