Editing Submarine (section)

====Overview====
[[File:USS Greeneville (SSN 772) - dry dock Pearl Harbor (1).jpg|thumb|The [[US Navy]] {{sclass|Los Angeles|submarine|0}} {{USS|Greeneville|SSN-772|6}} in dry dock, showing cigar-shaped hull]]

Modern submarines are cigar-shaped. This design, also used in very early submarines, is sometimes called a "[[teardrop hull]]". It reduces hydrodynamic [[drag (physics)|drag]] when the sub is submerged, but decreases the sea-keeping capabilities and increases drag while surfaced. Since the limitations of the propulsion systems of early submarines forced them to operate surfaced most of the time, their hull designs were a compromise. Because of the slow submerged speeds of those subs, usually well below 10&nbsp;[[knot (unit)|kt]] (18&nbsp;km/h), the increased drag for underwater travel was acceptable. Late in World War II, when technology allowed faster and longer submerged operation and increased aircraft surveillance forced submarines to stay submerged, hull designs became teardrop shaped again to reduce drag and noise. {{USS|Albacore|AGSS-569}} was a unique research submarine that pioneered the American version of the teardrop hull form (sometimes referred to as an "Albacore hull") of modern submarines. On modern military submarines the outer hull is covered with a layer of sound-absorbing rubber, or [[anechoic tile|anechoic plating]], to reduce detection.

The occupied pressure hulls of deep-diving submarines such as {{ship|DSV|Alvin}} are spherical instead of cylindrical. This allows a more even distribution of stress and efficient use of materials to withstand external pressure as it gives the most internal volume for structural weight and is the most efficient shape to avoid buckling instability in compression. A frame is usually affixed to the outside of the pressure hull, providing attachment for ballast and trim systems, scientific instrumentation, battery packs, [[syntactic foam|syntactic flotation foam]], and lighting.

A raised tower on top of a standard submarine accommodates the [[periscope]] and electronics masts, which can include radio, [[radar]], [[electronic warfare]], and other systems. It might also include a snorkel mast. In many early classes of submarines (see history), the control room, or "conn", was located inside this tower, which was known as the "[[conning tower]]". Since then, the conn has been located within the hull of the submarine, and the tower is now called the [[Sail (submarine)|"sail" or "fin"]]. The conn is distinct from the "bridge", a small open platform in the top of the sail, used for observation during surface operation.

"Bathtubs" are related to conning towers but are used on smaller submarines. The bathtub is a metal cylinder surrounding the hatch that prevents waves from breaking directly into the cabin. It is needed because surfaced submarines have limited [[freeboard (nautical)|freeboard]], that is, they lie low in the water. Bathtubs help prevent swamping the vessel.