Several major and large numbers of minor improvements were progressively introduced to Mk IXs , some of which were used on other Spitfire variants .
Production of the Mk IX finished at Supermarine in June 1943 , with production continuing exclusively at the Castle Bromwich factory .
Several major and large numbers of minor improvements were progressively introduced to Mk IXs , some of which were used on other Supermarine variants .
Production of the Mk IX finished at Supermarine in June 1943 , with production continuing exclusively at the Castle Bromwich factory .