Heavy Graviton Beam .
This weapon was originally designed after the Wolf 359 incident and is specifically designed to do extreme amounts of damage to Borg vessels. Based around a plasma weapon it uses a heavy Gravity field. Shields use a subspace harmonic to create their cohesion. It has been found that a shield can be rendered useless in heavy graviton fields and Starfleet recognised this as a potential weakness. If the frequency is correct you can distort another ships shields without affecting your own. In essence this is how the Heavy Graviton Plasma driver works. The actual Plasma weapon is a very crude, high power phaser (of sorts) which although not as highly tuned as the type X phaser array can do awesome amounts of damage. If the ship it is firing at has shields it does very little damage. However in conjunction with the Heavy Graviton distortion driver the result is very similar to a Quantum Torpedo. The tuned plasma literately goes straight through the outer shields of the ship and tear into the hull do masses of damage.