The J-1 semi-autonomous proton cannon functioned as a long-distance, self-propelled artillery piece deployed by the Confederacy of Independent Systems throughout the Clone Wars conflict.
This formidable heavy droid cannon could be operated by a single B1-Series battle droid positioned in a side-seat, or alternatively, by pre-programmed droid brain systems. Unlike automatic weapons, it employed a single-shot breach-loading mechanism. To fire, at least two battle droids were required to manually load shells into the breach before each shot. The shells possessed sufficient power to penetrate the shields of an Acclamator-class assault ship or obliterate a LAAT/i Gunship with a direct impact.
The artillery weapon, visually similar to a flak gun, was mounted atop four legs, bearing resemblance to the design of Advanced dwarf spider droids. This leg configuration enabled the cannon to rotate and reposition itself, however, its rotation speed was limited, as the legs served as the sole means of turning.
These artillery units saw action during the Battle of Ryloth in 22 BBY, where they engaged the invading Republic forces. In mere seconds, three of these cannons successfully destroyed a warship.
Due to the substantial damage inflicted upon the fleet and the shells' ability to bypass shields, Mace Windu issued an order to retreat. During the operation to liberate prisoners, Obi-Wan Kenobi, assisted by Waxer and Boil, commandeered one of the cannons and used it to eliminate the remaining artillery pieces before being forced to abandon it due to incoming fire from an AAT.
The proton cannons were later utilized by Geonosians during the Second Battle of Geonosis, where they were responsible for destroying numerous Republic LAAT/i and LAAT/c gunships.
In LEGO Star Wars III: The Clone Wars, the J-1 functions as the artillery choice for players fighting for the CIS in large-scale conflicts, serving as a counterpart to the Republic's AV-7.
LEGO Star Wars 7869: Battle for Geonosis, a LEGO set launched in 2011, included a model of this cannon that could launch a missile, featured poseable legs, and offered adjustable elevation and depression. The set also contained a BARC Speeder, Captain Rex, Luminara Unduli, a super battle droid and two B1 battle droids.