In the fourth year before the Battle of Yavin, the Galactic Empire operated a base on the planet Imvur, in the Hasmir system. Its C.O. was an officer named Viggen. At some point, the base was raided by Commander Ryden's rebel cell, who had secret headquarters on Imvur. Viggen sought to enact vengeance by tracking down the rebels to their base and attacking them. Although the Imperials could not prevent Ryden and his men from escaping in an evac ship, the rebel headquarters were abandoned. Some time later, six cadets from an Imperial Academy and their supervisor were dispatched to the Imvur base.