The Incredible Mr. Limpet(1964)

Don Knotts is Henry Limpet, a near-sighted office worker during World War II. Married, and he loves fish.

One day, he and his wife and navy buddy, George Stickle (not pickle), are down at the docks. He wishes to be a fish and becomes one—an animated one.

He meets another fish – a real cutie, he calls “lady-fish” and a crusty old crab. When America enters the war, he decides to lend a hand. Goes to a navy ship and offers to act as a guide to find U-boats. George becomes his liaison to the higher-ups.

The Germans wonder what this “limpet” is that keeps sinking their subs. They think it’s a mine and develop a torpedo to home in on the “throm” – the thunderous sound – Henry can make.

As Henry leads the fleet, he loses his glasses, and his crab friend comes along to act as his eyes. The Germans fire their torpedoes, but once he figures out how they work, he leads them back to the subs!

Henry returns to the dock where he fell into to see his wife one last time, and she brings him his spare pair of glasses; he and Lady Fish leave.

The story jumps ahead to the present. George and his old Skipper (both old and gray) have been ordered to find Limpet. They go to the area in the Bahamas where Henry first contacted their ship. There, they see him, make him a Commodore in the Navy Reserves, and ask him about particular dolphin activity.