[Smithy]

Hi Adam,

Back armour was initially not included on the Spitfire I and Hurricane I as the powers that were at the Air Ministry thought that its inclusion would adversely affect the balance of the aircraft.

It appears that in early 1940 1 Squadron in France were the first to fit back armour by installing this from a crashed Fairy Battle. A pilot from the squadron was later dispatched to Farnborough and performed an aerobatic display to demonstrate that aircraft balance had not been affected by the addition of back armour. After this back armour fitting became standard (unfortunately I do not have a firm date for this)

Also, which might interest you, back armour was 6mm thick.

Hope that helps,

Tim