The Spitfire MkV...
In parallel with Supermarine, Rolls-Royce were further developing the Merlin engine and in 1941 the Merlin 45 was available. It still retained a single stage supercharger but provided more power and ran higher manifold pressure. This produced the Mk V Spitfire which was available in three basic versions, Va, Vb and Vc, the principle difference being in their armament. The Va retained the eight .303 machine guns of the Mk1, the Vb with two Hispano-Suiza cannon and four .303 machine gun. The Vc had a more advanced wing which was not only stronger but also made possible the installation of four 20 mm cannon or two 20mm canon and four machine guns. This was know as the 'universal wing' , was a major step forward, and paved the way to the Mk IX Spitfire.
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