The cannon is a large building that fires a sustained particle beam up to an orbital mirror that reflects the beam back down onto enemy positions. The mirror can be remote-controlled by the commander to slowly move the beam, hitting more than one target.
General Alexis Alexander is most famous for employing this weapon on a large scale as her version comes at only half its usual cost. Laser General Townes has three in Fort Union, which is ironic because the Particle Cannon has nothing to do with the laser technology adopted by him. Chinese General Leang has access to use them as well.
According to one of General Ironside's unused taunts, the Particle cannon is a top secret weapon, and he ponders out loud as to how someone like the player could obtain one.
Particle Uplink Cannon
When fired, the Particle Cannon will direct a concentrated beam of high-energy particles into space. There, a satellite in orbit will reflect the beam and direct it onto the target, generating enough heat on impact to destroy all but the most fortified structures. The targeting satellite can be adjusted while firing, allowing a commander to slowly move the particle beam over the ground from one target to the next as it fires.
The Particle Cannon building is a high profile target. It consumes lots of power and ceases to charge if sufficient base power levels are not maintained. Unlike the other superweapons, the Particle Cannon is only useful for precision strikes, and is unable to destroy many buildings in a row let alone an entire base. While it is useful for destroying power plants or certain stretches of a defense line, it requires several simultaneous deployments before it can destroy a base. However, it has the shortest recharge time of all superweapons with only 4 minutes and therefore can be used more often. The Particle Cannon is also the most convenient to use when defending a base as it is the fastest superweapon to strike the targeted area after being applied.
If the player double-clicks while steering the beam, it moves faster (even being able to go faster than a Raptor or a MiG).
General Townes originally was going to have a Laser Uplink Cannon which was weaker than the Particle Cannon but with a longer duration, and it was going to be available earlier in game, when an Airfield is built. It was replaced by the Particle Cannon in the original game.
If a base loses power just as a Particle Cannon is being fired, the beam will instantly be cut off, and will not continue firing as soon as power is restored.
The Particle Cannon is effective against the GLA as it has the highest chance to destroy both the building and the GLA Hole.
If the player uses the Particle Cannon while playing as the GLA, Kanwar Khan will warn the player that their enemy is using their Particle Cannon, even though the player is the one who is using it.
While the particle weapon itself is perfectly possible, the way it is described in the game - surface-orbit-surface weapon - is completely unrealistic. It is impossible to reflect particle beam by "mirror" on satellite; while charged particle beams could be reflected by magnetic fields, electrostatic repulsion of equally charged particles make the charged particle beams disperse fast in space, thus limiting their use for atmospheric-only conditions. And neutral particle beams could not be used in atmosphere, being strictly vacuum weapon. On the other hands, surface-space-surface array is perfectly suited for lasers.