The Yamato weapon is a concept in science fiction. The name is used for a weapon that is extremely powerful but requires considerable time to charge while leaving the ship powerless and vulnerable.
The concept was introduced in the Space Battleship Yamato anime series, hence the name. In the original Yamato, the weapon was called a "wave motion gun", and was capable of wiping out entire space fleets. Larger versions of the wave motion gun were capable of destroying planets.