Part of Mortensen's training involved diving and swimming in very cramped spaces in order to simulate the rescue's actual conditions. Thankfully, these conditions were simulated with professionals, but there were times that it felt all too real:
"There were a lot of places that were so narrow that you had to just wiggle through. Sometimes you had to take your tank...off, while you were underwater, without disconnecting from the air — then go through this wiggle area, [and] put the tank on. Do this all calmly. We had two tanks. If something went wrong with one, just be calm. Don't freak out, because you can drown in a few seconds. Once you freak out and you swallow a little water, you're done. Even though it's a movie ... nobody can get to you fast enough, and so forth."
This led to a moment, Mortensen explained, where he accidentally rolled onto one of his oxygen tanks, turning it off in the process. He explained that he tried to remain calm and eventually was able to revert to his other tank, but there was a moment that felt like nothing he'd ever felt before. While he was thankfully able to get things back under control, this incident serves as another reminder of just how important proper safety protocols and training are on film sets. Without the expertise of the real-life divers, things could have gone much differently.
"Thirteen Lives" will premiere on Prime Video in August 2022.