Complex sentence: One E.P.9 "N747JC" had a more chequered career and was one of two evaluated by the British Army Air Corps with serial "XM819".
Split into simpler sentences: One E.P.9 "N747JC" had a more chequered career. Today, registered as "N747JC", this particular E.P.9 was one of two evaluated by the British Army Air Corps with serial "XM819".