Complex sentence: The delay at the rendezvous had resulted in clouds and drifting smoke from fires started by a major firebombing raid by 224 B-29s on nearby Yahata the previous day covering 70% of the area over Kokura, obscuring the aiming point.
Split into simpler sentences: The delay at the rendezvous had resulted in clouds and drifting smoke from fires started by a major firebombing raid by 224 B-29s on nearby Yahata the previous day over Kokura. The clouds and smoke resulted in 70% of the area over Kokura being covered, obscuring the aiming point.