Complex sentence: He claimed 12 fighters of the United States Army Air Forces (USAAF) shot down during April and May 1944 and three times he had claimed three fighters shot down during single combat missions.
Split into simpler sentences: He claimed 12 fighters of the United States Army Air Forces (USAAF) shot down in the months April and May 1944. Three times he had claimed three fighters shot down during single combat missions.