P-39Q Airacobra is different from P-63 Kingcobra
A standard bomb holder is mounted on an axial line under the fuselage. It is possible to suspend bombs of caliber up to 500 pounds or an additional fuel tank.
Due to the small capacity of the internal fuel tanks, an additional fuel tank, often with a capacity of 75 gallons, was often hung under the Cobra fuselages. The tank was mounted on a standard bomb holder.