An aerial retardant delivery system comprising a retardant tank mountable in the fuselage of an aircraft. The tank includes a pressure opening in fluid communication with the fuselage such that pressure in the fuselage may act on retardant contained in the tank. The tank includes an outlet extending through a sidewall of the aircraft's fuselage, through which retardant may be delivered to a target. The system also includes a discharge gate operative to open and close the outlet. An actuation mechanism is disposed on the exterior of the tank and operatively coupled to the at least one discharge gate. A variable flow controller controls the discharge gate open position in order to provide retardant over a desired area of terrain. A one-way flapper is disposed in the pressure opening and is operative to allow pressure in the fuselage to enter the tank while inhibiting retardant from spilling from the tank.