User blog comment:Owlfeathers0117/New RP Weapon Classification System/@comment-27820070-20150105071701/@comment-11135771-20150105154355

They're called Yamato Cannons because the Terran Dominion is based off a faction from Starcraft with the same name, and their capital ships carried a centrally mounted energy weapon called a Yamato Cannon. I believe the name was originally a reference to Space Battleship Yamato, in which the titular vessel was armed with a similar directed energy weapon.