Deadly Weapons
Sadly, animals, especially sea animals can be used for the worst purpose of them all. They can be equipped with explosives and they can carry the explosives to the enemy ships or submarines. The soldiers will not realize that the animal is dangerous so they will not react.
When the animal is close to the vessel, it can be detonated and it will destroy the ship. This is something that has been considered before with dolphins and even sharks. Even the United States Army had these plans.