"Every enlisted man in the Navy only gets 4-5 hours of a sleep a night" seems to be a common anecdote service-wide, including from people I know personally who served.
Also, "nights" are not a real thing, not in the biological sense.
In the surface ship nuclear power plant world where there is no air conditioning, you can't stand watch for more than 5 hours, which means 4 5s and one 4 hour watch. Think you stand the same watch every day? Nope, not enough people. You normally stand 1 on 2 off (5 and dimes) or one on 3 off (5 and 15s). This puts your sleep window at different spots every night.
Subs are air conditioned, so they can stand either 6 and 6s or less commonly 6 and 12s. Their lives are generally worse in every way.
Except they all like smelling each other farts and sharing beds, so it works out.
Subs are air conditioned, so they can stand either 6 and 6s or less commonly 6 and 12s. Their lives are generally worse in every way. Except they all like smelling each other farts and sharing beds, so it works out.