Plasma torpedo

"The Covenant cruiser came about to face them. Its plasma turrets glowed like angry red eyes."

- Description

The plasma turret, also known as a plasma cannon, is a weapon used by most Covenant warships. It fires magnetically guided bolts of plasma, referred to as plasma torpedoes, and can strike at almost any range. Along with the pulse laser turret and energy projector, it is one of their primary ship-to-ship weapons. Upon contact, a plasma torpedo causes severe damage to the target, boiling armor or overloading shields. The weapon can be used in conjunction with pulse laser turrets and energy projectors to decimate entire UNSC fleets, and can be used in ground assaults as well.

Description
The turret itself is antenna-like in appearance and is often located along the lateral sides of the ship. The beam is red, purple, or blue and short with a ball-like head and a trail. The turrets, from afar, usually appear as short spikes on the sides, the upper sides, and the bow of the vessel. On larger ships, the plasma is collected into visible lines located along the surface of the exterior hull before firing.

The size and power of the plasma turret depends on the vessel; the plasma turrets mounted on smaller ships such as corvettes are less powerful than those on larger vessels such as battlecruisers. In addition, the plasma turrets mounted on corvettes only appear to be able to fire their torpedoes in a straight line, while the tracking systems on larger warships are far more sophisticated.

Operation
Plasma is heated in a pinched magnetic field by energy supplied from the ship's pinch fusion reactors. The atoms that are on an appropriate trajectory between the Covenant starship and its target are then herded towards the mouth of the turret through a series of plasma conduits by magnetic pulses. Magnetic coils shape and guide the plasma, acting as a sophisticated focusing lens. When the weapon charges, a line of superheated plasma forms alongside the exterior plasma conduit adjoining the turret. Once fully charged, the line detaches and fires outward at its target. The torpedo is guided towards its target by a long-reaching magnetic field projected by the emitter. Upon impact, the torpedo penetrates the target starship, burning through internal decks and structures, thus causing heavy damage on the target.

They are extraordinarily accurate; one of the only ways for UNSC ships to even temporarily avoid them is to use emergency thrusters to "dodge" incoming torpedoes at the last moment. Particularly strong magnetospheres, such as those of gas giants, will disrupt the magnetic field holding the torpedo together, dissipating the plasma and rendering the torpedo harmless.

Plasma torpedoes are manually guided from a weapons control station on the bridge, by using holographic "steering spheres" superimposed over a holographic display of the space surrounding the ship. The plasma torpedoes and steering solutions of an enemy ship are similarly shown on the display. Covenant corvettes also feature manned control stations from which each turret can be operated individually. The Covenant have also developed "counter guiding signals", a form of electronic countermeasure that disrupts the guidance control of an enemy ship's plasma torpedoes.

The attacking ship must lower a section of its shield in order to fire the torpedo, otherwise it would detonate inside the protective barrier. John-117 used this weakness to temporarily blind a Covenant cruiser with a Longsword and to penetrate the shields of the Covenant supercarrier Ascendant Justice.

If the firing ship is destroyed, all plasma torpedoes guided by its magnetic fields are detonated prematurely or fly about aimlessly. However, it appears that torpedoes are sometimes able to hold together for a small amount of time, as demonstrated during the Fall of Reach, when fired torpedoes destroyed UNSC orbital defense platforms even after their firers had been destroyed.

As with virtually all of their technology, the Covenant themselves only understand a fraction of the underlying science involved with the operation of the plasma turret. As a result, despite their overwhelming power against human ships, the Covenant's methods of using their weapons systems are highly inefficient, relying on crude brute-force calculations and causing wasteful energy expenditure due to their slow operation. When in control of the Covenant ship Ascendant Justice, UNSC AI Cortana was able to use the vessel's plasma turrets to their full potential; she created an entirely new system to control the plasma, using electromagnetic pulses to direct the plasma atoms into precision beams within a microsecond. This enabled her to use the weapons with far greater power and precision than the Covenant themselves, cutting through Covenant vessels like a scalpel, not unlike an energy projector. According to Cortana, she could have improved the plasma turrets even further had the Covenant ship possessed better electromagnetic systems.

The magnetic coils used in a MAC gun can be used to shape and guide the plasma fired by a plasma turret; this was seen before the Massacre at Eridanus Secundus, when the 's magnetic coils were used to guide plasma generated by the Ascendant Justice's plasma turrets.

Tactics
Volleys of plasma torpedoes are frequently the first attacks launched by Covenant fleets when engaging enemy forces at long range. They often decimate enemy ranks upon impact. They emit visible radiation, giving them an amber color but volleys are visually akin to solar flares due to the sheer number of torpedoes launched. It has been said a single volley can destroy a ship from bow to stern.

Occasionally, plasma torpedoes can miss their target and fail to reacquire them if the target is moving towards the launcher at an oblique angle and high speed, such as the offensive maneuver conducted by John-117 to evade the fire of the Covenant ships at Alpha Halo during the Skirmish over Threshold, or also if the movement of the craft is erratic such as the way Keyes evaded the torpedoes during the Keyes Loop by detonating the ship's emergency thrusters seconds before impact. Even though they are considered very accurate against capital ships and space stations, they can frequently be evaded by smaller craft, such as Pelican dropships and Longswords.

Trivia

 * Captain Keyes once said "that couldn't have been a plasma torpedo or we would be free-floating molecules..." implying that even a single, well placed, plasma torpedo can destroy a UNSC vessel, even one as strong and stable as the Pillar of Autumn, though it could have been due to the fact that the Pillar of Autumn had already taken extensive damage during the Fall of Reach. Numerous plasma torpedos are seen in a later cutscene actually striking the ship, without destroying the Autumn.
 * The novels describe plasma torpedoes as being red, while in the games, they are blue.