Why The Spitfire’s Cannons Were Useless

The Supermarine Spitfire is a legend of the Battle of Britain, but its early cannon upgrades were a disaster in combat. Though it would become one of the war’s most iconic fighters, the road to effective firepower was anything but smooth.

A Machine Gun Start

When the Spitfire Mk I entered service, it was armed with eight .303 caliber Browning machine guns. Firing over 1,100 rounds per minute each, they were designed to overwhelm enemy aircraft in a brief 2-3 second firing window. But these rifle-caliber rounds lacked hitting power.

They could pepper enemy planes, but unless a vital component was hit, the target often kept flying. Against increasingly armored German bombers, the Spitfire’s firepower was beginning to look inadequate.

Cannon Chaos

The solution seemed obvious: upgrade to 20mm Hispano cannons capable of firing explosive shells. But fitting these large weapons into the Spitfire’s slim wing caused major issues. The cannons were mounted sideways with limited ammunition—only 60 rounds per gun.

Worse, they frequently jammed under G-force, often firing just one or two rounds before failing. Pilots of 19 Squadron, the first to test them in combat, were furious and demanded their older machine gun-armed Spitfires back.

Slow Progress, Painful Lessons

During the Battle of Britain, cannon-armed Spitfires were shelved. It wasn’t until the Mk V variant that cannon integration matured, using belt-fed mechanisms to reduce jamming and allow up to 135 rounds per gun.

Later Spitfire marks balanced cannon firepower with either .303s or .50 caliber Browning machine guns, providing versatility and much-needed reliability.

Final Form

By the war’s end, the Spitfire Mk 24 carried four 20mm cannons in redesigned wings, finally delivering the punch RAF pilots had long needed.

But early on, the Spitfire’s cannons were more trouble than triumph—leaving brave pilots to fight history’s most decisive air battles with underpowered guns and a whole lot of skill.