What the parent is saying is that diesel subs don't get to stay down like nuke subs. Nuke subs regularly stay underwater for the duration of their deployments,

What the parent is saying is that diesel subs don't get to stay down like nuke subs. Nuke subs regularly stay underwater for the duration of their deployments, which last months. Diesel subs cannot stay underwater for very long at all. We're talking on the order of hours.