Complex sentence: According to Luckner, the ship was struck by a tsunami which wrecked "Seeadler" on the reef, but some American prisoners alleged that the ship ran aground while the prisoners and most of the crew were having a picnic on the island.
Split into simpler sentences: According to Luckner, the ship was struck by a tsunami which wrecked "Seeadler" on the reef. Howver, some American prisoners alleged that the ship drifted aground while the prisoners and most of the crew were having a picnic on the island.