That's them picking definitions. The ship stayed submerged the whole time. They just poked their periscope out and vented for air once a day or so. There was no

That's them picking definitions. The ship stayed submerged the whole time. They just poked their periscope out and vented for air once a day or so. There was no other way to do it at the time. They surfaced once for a medical evacuation of a sailor - they didn't have to do that so I don't think that counts.