Everyone knows, or has at least heard from any number of SEALs and others in the media, in books and in movies, that Basic Underwater Demolition/SEAL (BUD/S) training is the most physically demanding training regimen in the world. This is of course debatable, as other U.S. military courses, and some foreign military courses for that matter, might rival BUD/S in difficulty. That is neither here nor there. I am not going to argue the suck level of each in turn in an pointless attempt to find the winner of the “hardest training” award.

I am here to regale you with some training horror stories from one phase of BUD/S training—second, or dive phase—that may or may not swing your opinion one way or the other in terms of what you think is the hardest training program in the world. Either way, BUD/S is a giant kick in the jewels, as evidenced by these 10 ways that second (dive) phase almost killed me:

1. The “Ice Boat”

This truly sadistic torture device—er, “cold-water conditioning tool”—was nothing more than an inflatable boat filled with ice that trainees were made to lie in for extended periods of time. I am fairly certain my reproductive organs made their way up far into my upper stomach region in their futile attempt to stay warm and preserve my future offspring. Brutal.

2. The 5.5 nautical mile swim

This one doesn’t sound so bad, right? A leisurely swim off the coast of Coronado, California, in the warmish fall air, staring at your swim buddy for four hours straight while your wetsuit top chafes the skin off of your armpits. Throw in 65-degree water and some rolling swells, and you might find yourself seasick, like me, vomiting between strokes as you try desperately to make the cutoff time for the swim while praying that a shark bites you so that you can end the ordeal. After all, you are chumming for sharks, anyway, with your vomit. At the end of the swim, you crawl out of the ocean barely able to move, and eat two MREs to replace the 4,000 calories you just burned.

3. Treading water with twin 80 SCUBA tanks

Treading water is really not that hard, and can be done for a long time assuming you have full use of your arms and legs, and minus any kind of significant weight driving you down below the surface. Unfortunately, none of these caveats apply to treading water in the pool during second phase of BUD/S. You can only use your legs, with hands above the surface at all times, and you have two SCUBA tanks strapped to your back. Good times. Mouths above water, gents!

4. Pool competency

This sounds so clinical, so very pedestrian. Of course I am competent in the pool. That should not be hard to prove, right? Wrong, Mandingo. This is the big crucible of second phase, and accounts for many a roll-back of otherwise very promising BUD/S students. It is a test of supreme patience and comfort underwater, as each student crawls along the pool bottom, struggling to overcome various “problems” inflicted upon him by circling instructors. Air is removed via diabolical knots and manhandling, and the students must overcome and stay calm under the surface. Once you complete the prescribed sequence of events, you can surface, but only in the specified manner. That is assuming you ascend under your own power, of course, and are not dragged up semi-conscious and half-drowned. Really good times.

5. Diving physics and medicine

Okay, so this is more of a metaphorically life-threatening aspect of second phase. In other words, you are physically and mentally taxed at this point in BUD/S, and you have to sit in a classroom and listen to hours of diving physics and medicine lectures. Then, you are tested on them. You must pass the written tests to move on to pool competency. Exhausting.

6. Breath-hold ascent training

Before you can get in the pool with compressed air on your back, where an uncontrolled ascent may very well injure or kill you via various diving-related physiological stresses, you are required to show you can ascend in a dive tower after taking a large breath of compressed air—where an uncontrolled ascent may very well injure or kill you via the same methods. But don’t worry, there is an instructor that will ascend with you and punch you in the gut if you are failing to exhale properly.

7. Closed-circuit dive training

After you master pool competency and the various classes that accompany it, you are lucky enough to begin closed-circuit dive training. This entails strapping a re-breathing device to your chest, breathing pure oxygen at depth (it’s poisonous at certain depths, over a prolonged time), and relying on granules in a canister to scrub the CO2 out of the air you exhale so you can breath it again. What could go wrong? Oh yeah, you have to navigate underwater, for thousands of yards, at night, with a compass board, while counting your kicks for distance. Super good times.

8. Jock-up drill

This sounds fun, right? Brings to mind good ol’-fashioned tomfoolery and lighthearted hazing, right? Wrong again. Imagine BUD/S calisthenics and PT, then add SCUBA gear and a mask full of water. Welcome to hell, you sons o’ bitches!

9.  Mask march

Hey, what could be worse than PT while jocked up in your dive gear? A forced march while jocked up in your dive gear! What could be worse than that? Fill your mask with pool water and proceed to march on. If you inhale the water, you have to refill it with ocean water. Who does this? BUD/S students, that’s who.

10.  Embolisms

Okay, these did not almost kill me, but they almost got my barracks mate and one of my best friends in the class. Both had to go to the decompression chamber following underwater incidents. My roommate never fully recovered mentally, and was medically disenrolled from BUD/S. My other buddy did recover, after crapping himself in the pool, and went on to become a successful SEAL officer.

BUD/S sucked, everybody. These are just 10 examples of how one phase of the training did its best to beat us down. It is not for everybody. Hooya.

This article was originally published in 2015. Author Frumentarius is a former Navy SEAL and a former Clandestine Service officer with the Central Intelligence Agency’s Counter-Terrorism Center. He has a Bachelor’s degree in International Politics and a Masters in History. He is currently a professional firefighter. Follow him on Twitter @SOFFru1