> When the sub is underwater, they can run very silently and be completely silent when they stop.
True, but diesel boats normally run on the surface, and on diesel, because battery life is limited; they generally submerge only to run an attack or to escape an attacker (or briefly at dawn, in case there's an unpleasant surprise out there that wasn't picked up). That's why nuclear submarines were once referred to as the first true submarines, as opposed to mere submersibles.
Modern air independent propulsion equipped diesel electric submarines have underwater endurance for several weeks. Even if they sprint full speed non-stop they could stay submerged several days.
True, but diesel boats normally run on the surface, and on diesel, because battery life is limited; they generally submerge only to run an attack or to escape an attacker (or briefly at dawn, in case there's an unpleasant surprise out there that wasn't picked up). That's why nuclear submarines were once referred to as the first true submarines, as opposed to mere submersibles.