Full text for submarine on the master keyword list:
A ship with this keyword printed on its deckplate card has removable hull pieces that are treated exactly the same as masts on a normal ship. At the beginning of your turn, decide if the submarine is submerged or on the surface. If submerged, lift the submarine’s hull from its base so only the “spine” is showing (the hull is set aside, and is still used to track damage to the submarine). When the submarine is on the surface replace the hull (minus any previously eliminated hull pieces). If submerged, a submarine can only move; it cannot shoot or be shot at, it cannot repair, it cannot dock, and it cannot be rammed. A submerged submarine may ram another ship, but regardless of success it must immediately be moved S away from the target instead of boarding. If a submarine is on the surface it functions exactly like a normal ship, except that it cannot pin or be pinned, cannot tow or be towed, and is not damaged when rammed (it can still board and be boarded normally).