Cannon is a ship upgrade found on some military derelicts. This upgrade is always permanently installed, and therefore can not be towed. Once a vessel with the cannon upgrade has been commandeered it will be available to the player. The upgrade can NOT be scrapped or uninstalled from the ship (essentially blocking a ship upgrade slot), but also never deteriorates.
The cannon upgrade has two shots, and can be fully refilled in the modifications screen for 4 scrap.
The cannon is used to target and destroy a room, with the syntax "cannon <r#>", e.g. "cannon r3".
The effects are the following: The room is exposed to the outside, therefore sucking everything inside into space and eventually filling it with radiation. Doors connected to the room are randomly destroyed or opened and then destroyed, possibly causing adjacent rooms to also be exposed to the outside. Fixed elements in the room (like power inlets) have a chance to be destroyed (as they would with any space exposure).
The destructive effects of the cannon can be used to eliminate hard-to-kill enemies, such as swarms or slime. It is best done by herding the enemy, unless it's slime, into an empty room, and shooting it with the cannon. Moving drones away from the room is recommended in the event that the shell (or the RNG) decides to blow one or more doors open instead of just breaking them.