Colonial equivalent to the C-4 explosive used by the U.S. Military.
Sharon Valerii's Cylon persona planted five G-4 charges in the water tanks aboard Battlestar Galactica, which resulted in the loss of over 60% of the ship's water reserves.
G-4 explosives are located in small arms lockers, thus under the domain of the Master-at-Arms, who was Sergeant Hadrian at the time. (Water)