Complex sentence: On 6 March, Benbow and the Red Baron clashed again Guttman & Dempsey (2009), p.64--65, when nine F.E.8s of 40 Squadron fought five "Jasta 11" aircraft led by Richthofen.
Split into simpler sentences: On 6 March, Benbow and the Red Baron clashed again. Nine F.E.8s of 40 Squadron clashed with five "Jasta 11" aircraft led by Richthofen.