James Cameron certainly knows a lot about submarines, but if he says something factually incorrect then it’s factually incorrect, period. Carbon fiber does not have “no strength in compression” and it is used in compression in countless applications, for example airplane wings. Again, the fact that the sub - built at absurdly low cost for its size, built by a bunch of cowboys that didn’t know what they were doing - DID survive to 3.7 km deep on several occasions is proof sufficient. If CF had no compressive strength than the whole thing would have failed at a tiny fraction of that depth. If CF had no compressive strength then what kept the sub together during the successful dives? Hopes and dreams?

I’m not here to defend the decision to use carbon fiber, and as I’ve said I completely agree that there are many issues with using it in this application. Delamination, water ingress, bonding the titanium to the carbon fiber, difficulty of manufacture including varying layer thickness and voids, sensitivity to impact, the list goes on. But _those_ are the issues, not the compressive strength.

Speaking of which I heavily recommend reading interview the prime ancestor comment to this chain linked. It’s really clear he knows what he is talking about.