A submarine hull has two major components, the light hull and the pressure hull. The light hull of a submarine is the outer non-watertight hull which provides a hydrodynamically efficient shape. The pressure hull is the inner hull of a submarine that maintains structural integrity with the difference between outside and inside pressure at depth.
U-995, a U-Boat of WWII, showing the typical combination of ship-like non-watertight outer hull with bulky strong hull below
Type XXI U-Boat, late WWII, with pressure hull almost fully enclosed inside the light hull
A hull is the watertight body of a ship, boat, submarine, or flying boat. The hull may open at the top, or it may be fully or partially covered with a deck. Atop the deck may be a deckhouse and other superstructures, such as a funnel, derrick, or mast. The line where the hull meets the water surface is called the waterline.
Hull form lines, lengthwise and in cross-section
Ship above the water with the entire hull visible
Royal Navy World War II MTB planing at speed on calm water showing its hard chine hull with most of the forepart of the boat out of the water.