Nature creates such phantastic forms that men often took the most unbelievable for true. But the oarfish is the larges bone fish and not a serpant and the pistol shrimp is no submarine nor a full size sea battle.
On their long voyages through the seas men made most amazing observations which turned back home into tales of large sea snakes attacking ships. This tales of sea snakes or heavy battles without trace are based on optical and sound based misunderstandings, but some times as well on true miracles of the seas. Today, modern science tries to observe and interprete the true reasons.