Complex sentence: Barber is credited with the sole kill of Yamamoto by military historians, but officially he and Captain Thomas George Lanphier, Jr. were credited with half a kill each when Yamamoto's bomber was shot down in April of 1943.
Split into simpler sentences: Barber is credited with the sole kill of Yamamoto by military historians. Previouslly he and Captain Thomas George Lanphier, Jr. were credited with half a kill each when Yamamoto's bomber was shot down in April of 1943.