Complex sentence: He claims that there were six Americans on the island, including himself, and that they could call on two small L-4 scout planes, and two old minesweepers converted to coastal cutters and manned by Korean crews.
Split into simpler sentences: He claims that there were six Americans on the island, including himself. They could call on two small L-4 scout planes, and two old minesweepers converted to coastal cutters and manned by Korean crews.