The Yamato Gun is basically a nuclear explosion focused through magnetic fields.
The name of the Yamato Cannon may have been inspired by the 1974-75 anime series Space Battleship Yamato (alternately titled "Space Cruiser Yamato" or "Star Blazers" in English). In the anime, the remnants of the Battleship Yamato, which was actually a real Japanese Battleship used in World War II and sunk in 1945, is retrofitted with advanced technology and turned into a spaceship to defend humans from alien attack. One of the Space Battleship's main weapons is a huge "Wave Motion" gun which fires from the bow of the ship.
StarCraft
Yamato Gun
The Yamato Gun is a powerful weapon that focuses a nuclear explosion into a beam using magnetic fields. It deals 260 damage.