So you probably know that as you go deeper into the ocean the pressure increases from the weight of all the water above you.  So we did an experiment.  We took styrofoam coffee cups and decorated them before sending them 1300 m (4265 feet) below sea level.  When we brought them back up they had shrunk!   When a submarine dives deep it must have protection against the pressure of the surrounding water, otherwise the lungs of the people inside would shrink like the cups!  Submarines designed to travel to such depths have a hull of titanium which is stronger than steel.   So just how much pressure are we talking about?  For every 10 m or 33 ft of water depth the pressure increases 15 pounds per square inch (psi – a car or bicycle tire has about 35 psi on average).  So if we are going down to 1300 m we are looking at almost 2000 psi pushing in all directions on the cup!   That is one big dogpile of water!