"No discussion of the terran battlecruiser is complete without mention of the legendary Yamato cannon, a devastating plasma weapon with enough firepower to decimate cities. Mounted on the ship's prow, the big gun draws its intense power from the ship's power core, and then uses an intense magnetic field to focus a controlled nuclear explosion into a cohesive beam of energy. The cannon is so massive that it requires its own conversion generator and a dedicated fire-control station manned by nearly 100 gunnery specialists."
The Yamato cannon is mounted on the prow of battlecruisers, and draws power from their core. The cannon draws its immense power from the ship's core, and then generates a dense magnetic field to harness a controlled nuclear reaction, turning it into a concentrated energy blast that can destroy almost anything with a few shots, even enough to decimate cities. The cannon requires a huge energy reserve to fire, requiring its own conversion generator and a fire-control station manned by nearly 100 gunnery specialists. However, the effects make it worthwhile. When fully charged, the Yamato cannon has explosive force equal to a low-yield nuclear explosion.
By the Great War, recent research had led to the development of the weapon. In 2499, terran engineers were working overtime to retrofit existing battlecruisers with the weapon. Behemoth-class battlecruisers received such retrofits. This trend continued with the Behemoth-class ships present within the Dominion Fleet. Some of the older vessels were not upgraded due to costs and limited supply.
In both StarCraft and StarCraft II, the Yamato cannon's range of ten makes it an effective siege weapon, able to destroy stationary defenses and anti-air units out of their range, leaving the battlecruiser safe. However, it takes a few seconds to charge before firing once a target is acquired. Only the strongest units can survive a shot from a Yamato cannon. The Yamato cannon is best used to eliminate strong anti-air defenders, such as enemy battlecruisers, carriers, and void rays.
The Yamato gun is a possible reference to the title ship of Space Battleship Yamato and its wave motion gun and, indirectly, a reference to the Yamato-class battleship used in World War II, which were the biggest battleships ever created in their time and had the largest cannons ever to be used on a battleship.