Tarzan and the Foreign Legion (Tarzan, #22)

When the American bomber crashed in the jungles of enemy-held Sumatra, the survivors faced the perils of a completely unknown world...and the RAF colonel who had flown with them as observer seemed to compound their danger by going mad—stripping to a loincloth and throwing away his weapons except for his knife. But for Colonel John Clayton, Lord Greystoke, the hazards of wild beasts and a remorseless enemy were a familiar and joyously accepted challenge—a chance to return to his true identiy of Tarzan of the Apes.
Gathering a motley crew of allies of many nations, Tarzan worked a terrible vengeance on the occupying Japanese, led an epic trek to the coast—to a final ocean rendezvous with enemies human and inhuman.