How do submarines cope with the pressure of the deep sea?

Question: How do submarines cope with the pressure of the deep sea?
- Keywords:
  pressure,
  submarines
Asked by ltlupus1 to Ryan on 20 Jun 2011.
- Ryan Ladd answered on 20 Jun 2011:
  
  It’s only really submarines which have air inside that have problems with high pressures. This means that robotic submarines can almost go as deep as they like without any problems at all.
  
  Submarines with humans inside do have problems though, like you see in movies. They cope with these pressures by having extremely strong hulls and try to spread out the pressure as much as possible by having a cylindrical shape. The strongest submarines for going really deep are usually close to spherical.

Question: How do submarines cope with the pressure of the deep sea?