In order to maintain that perfect ratio of an equal number of submerging the boat and coming back to the surface, a submarine cannot weigh more than it displaces.
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While living in Jacksonville, between Mayport and NAS Jacksonville and the then-open NAS Cecil Field, there were lots of active duty Navy about. We started playing a lot of the on-base clubs and of all things, we had a following of some SEALs that were stationed there for a while. I once repeated the remark about 'jumping out of a perfectly good airplane', and one of them got a little hot under the collar. I'll beat the (&($($E%$R# @@!! out of the next guy I hear say that. That's nothing ! Try swimming out of a perfectly good submarine, you locked up in a torpedo tube with an E1 squid with his hand on the button !!!'