Shard cannon

Pulse beams are a form of used and equipped by Enforcers, large Forerunner machines designed to combat severe Flood outbreaks.

Overview
The pulse beam fires a rapid stream of small, red semisolid energy bolts. These projectiles are very similar in appearance to that of the Needler, but do not have the homing or explosive abilities that the Needler has. Once the projectiles have made punctured an enemy, they "shatter" within a few seconds, just like Needler rounds. However, pulse beams do not create the same explosion as Needler rounds do when stuck with 7 or more projectiles. They travel a considerable range and gradually lose altitude as they fly, giving Enforcers a decent advantage over the Flood as they can fire from long ranges and heights.

The Pulse Beam is designed to effectively combat the Flood by vaporizing the host bodies and Flood forms to prevent reanimation. Due to the sheer amount of projectiles fired at once, and due to the sharpness of the projectiles, the projectiles easily penetrate flesh and most armor. Presumably, the explosion caused by the projectiles also aids in shredding Flood biomatter.

Since the projectiles have high energy power, they are also useful for combating other sentient beings, such as Spartans and Elites. However, like other attached weapons, they can be blown off to render the Enforcer harmless. The pulse beam is only one weapon used by the Enforcers, and is generally intended for use against infantry. The weapon is mostly ineffective against vehicles, so a more suitable weapon is used in its place.

While the weapon can be deadly, it is generally weak if appropriately avoided. Individual projectiles are of little consequence, but the player should avoid being hit by multiple projectiles, as they easily bring down shields.

Gameplay
Enforcers generally fire pulse beams at infantry units only, saving the mortar weaponry for vehicle based units. When fired, waves of red projectiles are fired towards the Enforcer's enemies. These are difficult to dodge head-on, but can be easily avoided if there is suitable cover, or if the player keeps up a constant pace to the side. The weapon is used only against infantry, as it would be generally ineffective against most, if not all vehicles, as the driver or pilot is generally well defended or hidden from direct view. Therefore the Enforcer uses it's mortar-like weapon to combat vehicles.

The weapon can easily defeat weak, unshielded units, such as Grunts, and even Jackals can have trouble using their shield to effectively block the projectiles. When used consistently, the weapon can keep an unshielded or wounded enemy pinned down for a considerable amount of time, and can be very distracting and frustrating when trying to defeat the Enforcer. Therefore it is usually a preferable tactic to disable the Enforcer's weapons first.

Trivia

 * When fired, a rapid, pulsating beating sound can be heard, though to hear it requires the player to pay close attention during gameplay.
 * The pulse beams can be destroyed by the player, causing the Enforcer to rely on its other weapon systems.
 * The pulse beam has many other nicknames amongst players, such as "Enforcer Needler".
 * The Halo Encyclopedia suggests that the Covenant might have reverse-engineered the Needlers and Heavy Needlers from pulse beams.