Diving planes, also known as hydroplanes, are control surfaces found on a submarine which allow the vessel to pitch its bow and stern up or down to assist in the process of submerging or surfacing the boat, as well as controlling depth when submerged. Bow and stern planes Diving planes are usually fitted in two pairs, the bow planes at the front of the submarine and the stern planes at the rear. The stern planes function in much the same way as an aircraft's elevator. As the planes are a long distance fore-and-aft from the hull's centre of buoyancy, they introduce a pitching moment. Ballast tanks within the submarine adjust buoyancy to be neutral, making the boat controllable. The position of the planes controls the pitch of the boat and, with the forward motion of the boat, this controls depth. If not carefully controlled, this could lead to a 'porpoising' motion whereby the planesman continually hunts for a stable combination of depth and pitch. For easier berthing close alongside a jetty, submarines have used folding bow planes that retracted alongside the hull. Earlier submarines (to World War II) used vertical folding planes perpendicular to their surface. US submarines referred to this stowage as 'rigging' the planes, and 'tilting' for their control movement. Later Soviet submarines have tended to fold backwards, into recesses in the casing. Fairwater planes Simon Lake of the Lake Torpedo Boat Company was the first to develop planes that could control depth without introducing a pitching moment. Stern planes and rudder were mounted below the stern akin to a conventional ship. The depth control planes were mounted on the beam, so that they acted vertically, without the lever arm to introduce the usual pitch. Diving planes located on the sail (conning tower) are called fairwater planes on US Navy submarines. Fairwater planes do not pitch the ship up or down; they cause the ship to rise or sink on a level plane as they are operated. When operating beneath polar ice, a submarine with planes on the sail must break them through the ice when surfacing. From the they were arranged to be able to be pointed vertically upwards, rather than being rigged or folded in. Newer boats, starting with the third-flight Los Angeles class subs (or 688is) have eliminated the sail planes, and operate instead with bow planes. Controls From the outset, diving planes were controlled