R2-4B

This astromech droid was owned by Lorn Moonrunner, and was used to assist in flying the starship Refugee. R2-4B wore what appeared to be a standard restraining bolt, but Lorn had modified a detonation device to resemble the bolt. This was all a precaution taken in case the Empire should ever discover that Lorn - the former Imperial Major Corvus Langlier - was on Rhamalai. When this finally happened, shortly after the Battle of Yavin, R2-4B was confiscated and placed in the Imperial droid pool. When R2-4B had been placed in the garrison in Argona, it activated the programming which activated the detonator. The resulting explosion destroyed much of the Imperial garrison.

Source
Star Wars Adventure Journal Volume 1, Number 13