Complex sentence: The Japanese mounted a strong defense which downed two Superfortresses and damaged another 64 (another eight B-29s were lost to other causes) and the Americans claimed 18 Japanese fighter "kills" as well as another 30 "probables" and 16 damaged.
Split into simpler sentences: The Japanese mounted a strong defense that downed two Superfortresses and damaged another 64; another eight B-29s were lost to other causes. The Americans claimed 18 Japanese fighter "kills" as well as another 30 "probables" and 16 damaged.