Needle

A Needle is a crystal-like, bluish-pink projectile fired from various different Covenant weapons collectively called Needlers. Unlike most Human or Covenant weapons, the Needle possesses guided, fire-and-forget capabilities and an explosive payload.

Design
The Needle stands out somewhat in the family of Covenant ammunition. While so-called "fuel rod" weapons make use of a gas- or explosively-propelled depleted uranium projectiles in a manner familiar to Humans, and plasma weapons make use of magnetically-accelerated plasma driven by a laser, Needlers make use of technology barely considered for small arms. Each Needle consists of a cubic zirconium crystal shell (which is believed to contain boron and undergo plastic deformation during growth to create its blue-pink colour), two fluid reservoirs, a mixing chamber, a small rocket engine and fuel similar to a gyrojet's, a targeting computer and sensor, and a length of copper-zinc-aluminium-nickel shape memory wire running the length of the projectile.

When a Needler's trigger is pulled, a Needle is loaded into the weapon's firing chamber. There, its targeting computer receives data from an infrared, optical, and bioelectromagnetic sensor in the Needler's sighting system. Once the data has been received and the target lock verified, the Needle's rocket engine activates, firing the Needle from the weapon. While in flight, the Needle tracks the target's thermal, optical, and bioelectromagnetic signature, altering course as necessary by shortening or lengthening the shape memory wire. This causes the Needle to bend and alter course, turning it right, left, up, down, or in combinations of these. The rocket engine leaves a pinkish trail as the Needle flies, giving a tracer element to the projectile and allowing the shooter to follow the trajectory relative to the target in order to make corrections to his or her aim. Upon impact with the target, a delay fuze activates, giving the Needle extra time to penetrate. Inside the Needle, the contents of the two fluid reservoirs are mixed, which results in a powerful explosion that causes severe damage to the target. The zirconium crystal shell also shatters upon detonation, causing extra damage from fragmentation, and depending on how long the Needle has been in flight, its payload of rocket fuel is added to the detonation.

Most Needlers allow the Needle to be set in two modes: The most often used setting has been dubbed Long Delay High Explosive by the United Nations Space Command Defence Force and "supercombining" by UNSC soldiers. This means that the fuze of the first Needle fired is automatically set so that it has a longer delay than the last Needle to be fired, allowing the Needles to explode within the target consecutively to cause even greater damage. The time frame allows for for a maximum of seven to be inserted into the target before they all explode. The next group to be shot will 'reset the counter'. The second setting is dubbed Delayed High Explosive by the UNSCDF in which the Needle simply explodes shortly after impact. Curiously, recovered Needlers indicate that the weapon also allows for the guidance setting to be turned off. It is believed that this is due to the sense of honour exhibited by large numbers of Sangheili warriors, who may perceive a fire-and-forget weapon to be dishonourable and a destabilising element in an otherwise fair fight.

Needlers

 * Type-33 Guided Munitions Launcher - A pistol-sized weapon often used as a sidearm by Sangheili.
 * Type-31 Rifle - A rifle-sized weapon used in Designated Marksman roles by the Covenant.
 * Type-43 Anti-Air Launcher - An anti-aircraft artillery piece. Essentially a surface-to-air missile system.

Behind the Scenes
The information in this article originally came from a Halopedia Blog written by the author on the subject. It also incorporates ideas from Echo-77 response blog.