The Mark XII phaser cannon was a type of Federation particle weapon which had entered service by 2381. The phaser cannons were one of many experimental new technologies employed on Starfleet Vesta-class multi-mission explorers at that time, and gave that particular class of starship an edge in battles with Borg vessels during the Borg Invasion of 2381. (ST - Destiny novels: Gods of Night, Mere Mortals)