The gist of it is this: the article says that the Russians wanted to build a concrete submarine. The C-sub, they claim, can drop way below the depth that regular metal subs can–the so-called crush line. Furthermore, C-subs are harder to detect via sonar, because they fade into the background.
Now I haven’t read about this actually happening, but I did see a page where someone had actually built one. Whether it was successful or not, the article doesn’t say. But at least the idea, despite sounding like utter insanity, might be something else indeed. Google, by the way, pulls up over 1.5 million results for concrete submarines, so the idea may be more popular than you think.
[Link: Popular Mechanics]