Military diesel subs have snorkels so they can run their diesels when they are at periscope depth. If they need to go deeper (or don't want a radar-reflecting s

Military diesel subs have snorkels so they can run their diesels when they are at periscope depth. If they need to go deeper (or don't want a radar-reflecting snorkel sticking up over the surface) they shut down the diesels and rely on batteries. Traditionally huge banks of lead-acid batteries, not sure if newer subs use Li batteries.