We also did what was called crab fights in the 10ft tanks where 3 blindfolded divers would fight while air was turned on and off. We had to stop when someone paniced so bad they pulled a knife in the tank. But the idea of the drills was to enable you to function during the panic that ensues when you are drowning. You still have to be able to talk clearly to the top and rig your helmet without seeing. People panic when water is making it hard to breath or you are going on a minute thirty without taking a breath and your helmet is still flooded.
I would imagine this is very similar to waterboarding EXCEPT you are still under control. Having people hold me down and do this to me would suck very so much, especially if they could do it for as long as a I could stand without killing me. I am sure this did not happen to USmarine. He most likely got the very limited intro version, not the fucked with for hours to completely break his ass version. Panic is panic and they do it to induce panic. It is what it is. Call it torture, warm fuzzy torture, or not torture but there is nothing wrong with it when used to gain info from terrorists. It is humane to the point it sickens me that it is even being debated.