Complex sentence: During World War II he served with the 355th Fighter Group in the European Theater of Operations, where he flew P-51 Mustangs from July 1944 until February 1945 when he was shot down over Germany on his 52nd combat mission.
Split into simpler sentences: During World War II, he served with the 355th Fighter Group in the European Theater of Operations. He flew P-51 Mustangs from July 1944 until February 1945, when he was shot down over Germany on his 52nd combat mission.