For example, when we turn in a bike, we have to bend slightly inward for the centripetal force. However, considering there’s no concept of “ground” underwater, do submarines still have to bend inwards? If yes, is it for the same reason as bikes?
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My previous answer was removed, so I will copy and paste rather than linking, it was written by a redditor when this question was asked a while ago.
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Submarines (usually) do not have any roll control, only pitch (bow/fairwater and stern planes) and yaw (rudder). Submarines do roll during maneuvers, but it is an unintended and often undesirable consequence. When a submarine turns/yaws, usually the submarine initially rolls outboard because the center of buoyancy is above the center of gravity. The same is generally true for surface ships; they roll in the opposite direction of a turn.
When a submarine yaws, the sail and hull have a non-zero angle of attack relative to the oncoming water. Thus they begin to produce lift. The sail is above the hull, thus the lift it produces rolls the submarine. Often the roll is into the turn, so the submarine transitions from a roll outboard of the turn to quickly inboard of the turn. This phenomenon is often called “snap-roll.” (Due to the complicated vortical flows over the sail and hull, sometimes the roll due to the sail and hull is in the opposite direction; it’s a complicated phenomenon, especially with hulls that are not perfectly axisymmetric.)
Snap-roll is undesirable because the submarine is leaning into the turn and the rudders are now partially acting to dive the submarine. You could imagine that if the roll was 45 degrees (an extreme case), the rudders are now 50% turning the submarine and 50% diving it. Since snap-roll usually occurs at high speed, this sudden dive is not a welcome maneuvering characteristic.
There are many ways to reduce or eliminate this problem. The first idea was to blunt the trailing edge of the sail so that it would produce less lift. This was tried on the *Nautilus*, but resulted in vortex shedding and extreme vibration. The next solution was to install a “dorsal rudder,” a flap in the trailing edge of the sail, again to reduce lift in a turn. This was tried twice on the *Albacore*, but it did not work especially well and resulted in significant forces being applied to the sail structure.
One solution that did work was to adjust the areas and positions of the control surfaces and stabilizing fins at the stern to counteract the lift produced by the sail. Other submarines have stern planes that can operate independently, allowing enough roll control to counteract snap-roll. So some submarines do have roll control, but it is only to make sure the submarine rolls as little as possible.
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