A phase cannon was a phase-modulated energy weapon, a type of particle weapon which served as a successor to plasma cannons and as a precursor to the phaser of the 23rd and 24th centuries. The prototypes of ship-mounted phase cannons were first introduced by the Earth Starfleet in the mid-22nd century, designed as the primary defense of NX class starships and serving as a supplement for the lacking spatial torpedoes of the time. The first NX class vessel to test and actively use phase cannons in battle was the NX-01 Enterprise.