I thought it was SEALS training.
They lock you in a barrel and you have to hold your breath as it fills with water.
Ranger training pushes you to 75% Exhaustion, and in Special Forces training they drown you, literally, they drown you and revive you. They put a Plexiglas plate over your head and push you under water until you float up. Then there is the live training were you can die, blown up/shot.