Penguins as Torpedo?

The body of a Penguin is shaped much like a torpedo, allowing them to "fly" along in the water very efficiently (called "hydrodynamic").

The bones of a Penguin are solid (not hollow like most birds) which allows them to withstand great water pressure when they dive for food. Hollow bones would collapse and break in the pressures of diving in the ocean depths. (Emperor Penguins can dive as far as 900 feet down)

Solid bones also act as extra weight to help Penguins dive deeper.