The Irregulars was the name of a collection of small military units of the Alliance to Restore the Republic operating behind enemy lines from secret bases. Often disguised as criminals, merchants, and ordinary citizens, The Irregulars were known to attack less-defended military targets, including bureaucratic cores, factories, garrisons and space stations. They also robbed storehouses, jammed communications and terrorized, and sometimes killed, high-ranking officers, of the Empire.
As the Empire could not ignore these attackers, the only choice was to assign an overwhelming amount of resources to neutralize the badly-funded units. While doing so, the Empire was diverting their resources from other, more important jobs such as finding the Alliance commanders. The Irregulars ran when faced with opposition, forcing the Empire to search for their secret bases.