Fusion cannon
From MediaWiki
The Fusion Cannon is Megatron's ultimate weapon. It is attached to his right arm and is devastatingly powerful, as demonstrated by its sudden removal of Ironhide's head. (It's at least as powerful as Fortress Maximus' hands, then.)
Presumably, this cannon is powered by some sort of nucular nuclear fusion reaction. Sometimes Megatron has been able to link up extradimensionally to a black hole to augment this power, increasing it astronomically, and
making him look real cool and space-rippy in the process. Most bodacious!
Galvatron had a big cannon, too, but it didn't work by fusion.
