 The Spitfire, from about mid-1940, had 73 pounds (33 kg) of armoured steel plating in the form of head (of 6.5 mm thickness) and back protection on the seat bulkhead (4.5 mm), and covering the forward face of the glycol header tank.The Hurricane had a similar armour layout to the Spitfire, and was the toughest and most durable of the three.Serviceability rates of Hawker's fighter were always higher than the complex and advanced Spitfire.