There are many ways you can lay the smack down in uber-RTS, Supreme Commander. If you want to keep progressing in your campaigns of destruction, you better figure out how to use the Experimental Units, 'cause when you do, your enemies are in for a world of hurt. And then death.
The Fatboy is an amphibious mobile factory and weapons platform, kinda like a Metal Gear. Its hull is lined with a self-sealing compound that makes sure hull breaches are kept water tight. This compound along with a reinforced shell allows the Fatboy to traverse into very deep water where pressure would buckle ordinary vehicles.
The Fatboy's stock cannon is the future of UEF weaponry. Using a special coolant system, the rapid fire tri-barreled gauss cannon can fire 5 times faster than older gauss cannon technology, which is great if you can't wait for your enemies to die. Unfortunately, the gauss cannon cannot function while under water.
The single rear mounted construction bay allows the Fatboy to surface and immediately begin construction of a support force. Like the cannon, the factory aspect cannot operate under water. So you better make sure to get through the oceans quickly and set up on shore, otherwise you could be a sitting duck.