@PandaTar, yep. Fast attack subs - the small stealthy ones that do all the cool ops, but stay underwater for 6-7 months, and are very small - didn't seem much bigger to me than the old subs you see in movies. Have about 100 crew, but everyone hot-racks. Subs run on an 18 hour day instead of a 24 hour day. 6 hours for watch. 6 hours for maintenance. 6 hours for sleep, shower, training & qualifications. So, generally 2 to 3 people to a rack, switching out each 6 hours. And the racks are the size of MRI tubes. Just had a very long spinal MRI, so I can say that for sure.
If you're on a boomer (ballistic missile submarine), those things are like floating hotels (even bulkhead doors are 3 times larger) that only stay out 3 months at a time. I've been on one, but didn't get to tour the rack space and didn't think to ask my buddy about how they hot rack, so I don't know about those.