Complex sentence: During a battle the Chaplain had gathered some Marines together in prayer that a supposedly dead Japanese soldier used as a target for his hand grenade killing several, and wounding their sergeant with a spinal injury.
Split into simpler sentences: During a battle the Chaplain had gathered some Marines together in prayer. A Japanese soldier, thought to be dead, used the group as a target for his hand grenade, killing several and wounding their sergeant with a spinal injury.