Dogfights over the English channel showed the Spitfire Mk. V outperforming the Bf 109 E at the time and led to the Bf 109 F series. The Bf 109 F "Franz" series was a significant improvement over the Bf 109 E. It featured the DB 601 E engine, which boasted an over 25% increase in power. The F-4 was also fitted with the MG 151/20 cannon, which was a 20 mm cannon that could fire a variety of shells.