Groundcrew refuelling Spitfire Mk IIa P7420, Duxford
The early Spitfires, equipped with eight .303-inch Browning machine guns, were initially powerful fighters, capable of delivering a formidable punch. However, as World War II progressed, it became apparent that this configuration lacked the firepower needed to effectively engage modern bombers, which were now being outfitted with armor to protect both the crew and critical components. A heavier armament was necessary to bring down these more resilient aircraft.
The RAF had foreseen this need and selected the Hispano-Suiza 20mm cannon, a French-designed weapon, as the solution to the problem. This cannon had superior firepower, capable of delivering more destructive rounds compared to the .303 machine guns. Originally designed to fire through the propeller hub of a fighter’s engine, this setup wasn’t possible for the Spitfire or the Hawker Hurricane. Instead, the cannons had to be mounted in the wings of the Spitfire, with one placed in each wing beyond the arc of the propeller.
In June 1939, the Spitfire Mk I L1007 became the prototype for this new cannon-armed configuration. However, the Spitfire’s thin wings, which had been designed for machine guns, posed a challenge. The Hispano cannons had to be mounted sideways to fit, causing bulges on the wings to accommodate the ammunition magazines. This also led to the cannon barrels sticking out from the leading edge of the wings. Initially, these cannon-armed Spitfires did not carry machine guns, which affected their overall firepower in certain scenarios.
Early Trials and Problems
Early tests with the Hispano cannons were problematic. The wing’s flexing during maneuvers caused frequent stoppages, and if one cannon jammed, the asymmetrical recoil would pull the aircraft off its course, spoiling the pilot’s aim. The first recorded operational sortie by a cannon-armed Spitfire occurred on January 13, 1940, when a Heinkel He 111 bomber was attacked. Although hits were scored, the cannon jammed before the Heinkel could be destroyed, and it had to be finished off by other Spitfires with machine guns.
Despite this shaky start, the RAF was encouraged by the potential of the Hispano 20mm cannons and immediately set about resolving the mechanical issues. Eventually, modified Spitfires with two cannons but no machine guns were sent to No. 19 Squadron, which had to operate alongside Spitfires armed with the full complement of machine guns. These cannon-armed Spitfires were designated as Mk Ib, while those with the traditional eight machine guns were labeled Mk Ia from March 15, 1940.
Mixed Reception During the Battle of Britain
The cannon-armed Spitfire Mk Ib saw action in the Battle of Britain, but they did not make a significant impact and were generally unpopular among pilots. The cannons still suffered from jamming issues, and many RAF pilots, including Squadron Leader Pinkham of No. 19 Squadron, preferred the machine-gun-armed Mk Ia. Pinkham even requested that the cannon-armed Spitfires be reassigned to an Operational Training Unit (OTU), allowing his squadron to receive machine-gun-armed Spitfires, which he felt were more effective against the enemy. His request was granted by Air Chief Marshal Sir Hugh Dowding, the Chief of Fighter Command.
Continued Development and Success
Despite the initial lack of success, the RAF continued to work on improving the Hispano cannon system. By November 1940, a batch of cannon-armed Spitfires was issued to No. 92 Squadron, this time featuring a mixed armament of two Hispano 20mm cannons and four .303-inch Browning machine guns. This combination proved to be highly effective, and the cannon-and-machine-gun setup became the standard armament for many future Spitfires.
The success of this hybrid configuration demonstrated the Spitfire’s adaptability, and it helped solidify the aircraft’s reputation as a highly capable and versatile fighter throughout the war. The Spitfire Mk Ib, equipped with both machine guns and cannons, represented the RAF’s ability to innovate and overcome the technical challenges of integrating more powerful armament into a fighter designed during a different era of aerial combat.