Plasma Torpedo

The Plasma Torpedo is a Covenant starship-launched, super-heated bolt of plasma. They are mounted on the lateral areas of a Covenant starship and are used on almost all Covenant Starships including Frigates, Destroyers, Carriers and certain classes of Cruisers.

Plasma is heated in a pinched magnetic field by energy supplied from the ship's reactors. The atoms that are on an appropriate trajectory between the Covenant starship and its target are then herded towards the mouth of the torpedo tube by magnetic pulses. The plasma torpedo is then fired, and is guided towards its target by a long-reaching magnetic field projected by the tube. 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.

Upon impact, the torpedo penetrates the target starship, burning through internal decks and structures, thus causing heavy damage on the target.

Trivia

 * 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 a Covenant flagship's shields.
 * 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 the Master Chief to evade the fire of the Covenant ships at Alpha Halo during Halo: First Strike, 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.
 * Volleys of plasma torpedoes are frequently the first attacks launched by Covenant Fleets when engaging enemy UNSC 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.
 * If the firing ship is destroyed, all torpedoes guided by its magnetic fields are detonated prematurely or fly about aimlessly. However, in Fall of Reach, fired torpedoes destroyed UNSC Orbital MAC Platforms even after their firers were destroyed.
 * 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 took extensive damage during the Fall of Reach.
 * Though the novels describe plasma torpedoes as being red, in the games, they're blue.