This heavy droid cannon could be operated by one B1 battle droid in a side-seat, or by pre-installed droid brain. It did not have an automatic reloading chamber, but instead was a single shot breach-loader. Shells had to be manually loaded by at least two battle droids into the breach before each shot. The shells used were powerful enough to breach the shields an Acclamator-class assault ship or completely destroy a LAAT/i Gunship with a single hit.
The artillery piece, resembling a flak gun, was mounted on top of four legs, similar to that of Advanced dwarf spider droids, which allowed it to turn and re-position itself, however, its turning rate was quite slow, its legs being the only rotational device.
These units were used during the Battle of Ryloth in 22 BBY, where they fired upon the Republic invasion force. Three cannons managed to take down a ship within seconds.
Mace Windu ordered a retreat due to the damage the fleet was taking, as the cannon shells were able to penetrate the shields. During the liberation of the prisoners, Obi-Wan Kenobi took control of one of the cannons and destroyed all other cannons with help from Waxer and Boil before having to abandon the cannon due to incoming fire from an AAT.