The first aircraft to enter combat with the Hispano was a Spitfire IB flown by pilot Officer George Proudman of 111 Squadron. On January 13, 1940, Proudman joined a group of Hawker Hurricanes in attacking a Heinkel He 111, only for the starboard cannon to fail after firing one round! The port gun followed suit after delivering 30 rounds, prompting the Hurricanes to complete the attack.
In July 1940, 19 Squadron re-equipped with cannon firing Spitfires, even though the cannon were still less than reliable.
|“||The guns of about six of 19 Squadron's aircraft are working satisfactorily, and defects in the others will be rectified in a week or 10 days.... but I am not at all keen on sending them up against German fighters since it will be extremely badly equipped for the task. Air Chief Marshal Hugh Dowding's report to the Secretary of State for Air, 24th July, 1940 ||”|
Despite Dowding's misgivings, 19 Squadron's cannon Spitfires were able to participate in combat, albeit with limited effectiveness. On 16 August, the cannons were working in only one aircraft out of seven. Bu the 31st, it was three out of six, a situation which prompted the Squadron's Commanding Officer to suggest that the cannon equipped aircraft should be exchanged for aircraft with eight machine guns from an Operational Training Unit.
These drum fed weapons were later replaced by versions fitted with a recoil driven belt feed, developed from a design by Chatellerault of France. This modification led to the deletion of the slotted recoil reducing muzzle brake. Both versions of the Mk I Hispano was later replaced by the Mk V, which was shorter and lighter, due to deletion of the recocking device, combined with a 30cm reduction in barrel length.
The Hispano was described as having the impact of a 3 ton truck hitting a solid object at 50mph.