The Grand Cannon was a gigantic Reflex Cannon built on Earth during the First Robotech War. Located in the Alaskan wilderness, the top secret facility where it was built doubled as a United Earth Forces command center where meetings were held with both the military and political leaders of the United Earth Government.
Most of the base was constructed deep underground with only a handful of towers and a small landing strip to mark it's location on the surface. The shaft of the cannon is over six miles deep and a huge railway and elevator system is used to carry passengers through it. A cross section of the cannon resembles a funnel, with the shaft widening greatly at the top.
The Grand Cannon only fired once, destroying a significant portion of the Zentraedi Armada before being severely damaged by its own immense firepower.