William McRaven: As you get up underneath the ship, as you approach a ship, there’s a little bit of light above you. You can see it when you are underwater. But once you get close to the ship, the ship blocks out all the light, and the target for a ship is the keel, the center line of the ship. And as you get under there — one, ships have machinery, so there is a very deafening noise as well which can disorient you very quickly. So you have to maintain your composure, you have to be calm, you have to move to the center line. You cannot see anything. So it is so black you literally can’t see your hand in front of your face, so everything is by feel. And you also know that under a ship there are suctions which could, in fact, pull your facemask off or do some things. So you have to be very calm, very composed as you are making your way to the objective, even in a training environment. So this is another aspect of the SEAL training that’s very important is learning to keep your composure when things are very, very difficult. Again, that is something that will weed a guy. A lot of guys could do the physical part, but when they got to this part that — while it was still physical — it was much more mental. It’s about, “Don’t be afraid under a ship. Be calm, take care of business and then get out and then keep moving on.” So a lot of guys struggled with that and didn’t make it through that part of the training.