I don’t get why carbon fiber was used in the first place. The composite material is known for its great tensile strength: tensile as in tension, not compression. Carbon fiber is actually also known for being lousy at handling crushing (compressive) loads. If you crush carbon fiber, it’ll fail shortly after.

Going under water would place the vessel under compressive loads, which at a quick glance would be the wrong type of loads for carbon fiber. That’s my initial take on it, however I haven’t spent any real time trying to engineer one.