A few days ago I wanted to test the crush depth of my VIIC, it went to 410 meters before imploding! Of course, I had 100% hull integrity and I'm sure it would have imploded even if I would have started to go up again at 300 meters, damage would have been to bad to repair before I would have reached the surface.
Let's honor the crew that got lost with that dive, they gave their lives for a higher good and went this deep so others wouldn't have to...