Subs have very small arsenals of weapons. In a disaster I think you’d find it very hard to get hold on one quick enough to top yourself.
One things for sure, there’s not a normal gun in the world that could pierce a sub. Even a .50 would just bounce off
Advanced AP rounds would eventually get through some subs not sure about all - but not just 1-2 shots.
There is a video somewhere on YT of someone who finally does it from similar composition plate.