The Particle Cannon is the tier three super weapon for Allies. The Particle Cannon is extremely powerful like the rest of the tier three super weapons and is deadly against structures and any units that happen to be in the blast radius.
The Particle Cannon like the Chronosphere appears through the fog of war and it is very expensive so you want to absolutely be sure that you can protect it before spending your money on it. It also has a very long charge up time which does not make it very effective for multiplayer.