I like synthetic biologicals, drone whales, they look like whales, they have an exact acoustical signature as a whale, they can blend in with a herd.
But they can launch rocket powered anti ship torpedoes, nuclear tipped if needed.
Or syn dolphins, but instead are themselves anti ship mines.
And if you truly want to demoralize the enemy you create a huge robotic Kraken, ship sized.
Haha the kraken pushed me over the edge. I was chucking already, but lost it at that moment. I like your style.