Why were many Spitfires/Seafires equiped with two 20mm cannon when they could carry four? Was it to reduce weight, increase the amount of ammunition for the reduced number of cannons, pilot preference or other reasons? I can find no reason given at any internet site.
If you give a reason for this armament choice would you please site the source of your knowledge.
Check wikipedia for this.
In June 1939, a single Spitfire was fitted with a single drum-fed Hispano in each wing, an installation that required large blisters on the wing to cover the 60-round drum. The cannons suffered frequent stoppages, mostly because the guns were mounted on their sides to fit as much of the magazine as possible within the wing. In January 1940, P/O George Proudman flew this prototype in combat, but the starboard gun stopped after firing a single round, while the port gun fired 30 rounds before seizing.[77] If one cannon seized, the recoil of the other threw the aircraft off aim. Nevertheless, 30 more cannon-armed Spitfires were ordered for operational trials, and they were soon known as the Mk IB, to distinguish them from the Browning-armed Mk IA, and were delivered to No. 19 Squadron beginning in June 1940. The Hispanos were found to be so unreliable that the squadron requested an exchange of its aircraft with the older Browning-armed aircraft of an operational training unit. By August, Supermarine had perfected a more reliable installation with an improved feed mechanism and four .303s in the outer wing panels. The modified fighters were then delivered to 19 Squadron.[77]
More Spitfire Mk Vs were built than any other type, with 6,487 built, followed by the 5,656 Mk IXs.[90] Different wings, featuring a variety of weapons, were fitted to most marks; the A wing used eight .303 in (7.7 mm) machine guns, the B wing had four .303 in (7.7 mm) machine guns and two 20 mm (.79 in) Hispano cannon, and the C or Universal Wing could mount either four 20 mm (.79 in) cannon or two 20 mm (.79 in) and four .303 in (7.7 mm) machine guns. As the war progressed, the C wing became more common.[122] Another armament variation was the E wing which housed two 20 mm (.79 in) cannon and two .50 in (12.7 mm) Browning machine guns.
It was a case of just being in line of development. From 8 .303 Brownings, to 2 20mm Hispanos and 4 .303’s, and then 4 20’s and 4 .303’s. As the mission changed, the armament changed.
Thank you for your response but, it doesn’t answer my question which is: If the C wing could carry four 20 mm cannon why do many of the pictures I see show only two cannons mounted and two cannon bays capped off? Was this due to: differences in mission such as air-to-air combat as opposed to ground support; weight considerations; RNAF versus RAF requirements; or some other reason(s)?
Another questioned on this point just occurred to me. If cannons could be mounted in the B and C wings why were locations for machine guns kept? I read that during the Battle of Britain it was discovered that the .303 mg put holes in aircraft but allowed many aircraft to remain in the the air and return to France to be repaired and return to the Battle. Why not do away with the .303 mg positions and increase the ammo space for the cannon or go straight to the .50 in. mg. positions as in the E wing?