Imvur base was a facility operated by the Galactic Empire on the planet of Imvur, situated within the Hasmir system. This base was active from 4 BBY to 3 BBY. The C.O. in charge was an officer identified as Viggen.
Commander Ryden's rebel cell, which maintained a clandestine headquarters on Imvur, launched a raid on the base at one point. Viggen, seeking retribution, attempted to locate the rebels' base and attack them. While the Imperials failed to prevent Ryden and his group from escaping aboard an evac ship, the rebel headquarters were left behind. Later, a group of six cadets from an Imperial Academy, along with their supervisor, were sent to the Imvur base.
The Imperial base led by Viggen originally appeared in "Vulnerable Areas," a comic strip penned by Martin Fisher and illustrated by Bob Molesworth. It was featured in the seventeenth issue of the Star Wars Rebels Magazine. Although the story made it clear that the rebel base was on Imvur, the location of Viggen's base was not initially specified.
In "Academy Cadets," a story written by Fisher and illustrated by Eva Widermann for the Star Wars Rebels Magazine 18, an Imperial "base at Imvur" and its Commanding Officer were mentioned. Subsequently, Martin Fisher confirmed via Twitter that Viggen's base and the one established on Imvur were, in fact, the same location.