This part will allow your Emergency Alert vehicle to carry the G2P-001d Cannon accessory behind the lightbar.
Obviously, this part is optional to the kit. It will store in the same spot on the robot mode.
Additionally, this part will also hold any other third party customized accessory with a 4mm peg for other figures using the same mold. Hint: the accessory was in a "grey box" and it goes on a red version of the Emergency Alert figure.