He paused; then went on: I don't know that the commanding officer delved so deep as that into his feelings. But he did suffer from them—a sort of disenchanted sadness. It is possible, even, that he suspected himself of folly. Man is various. But he had no time for much introspection, because from the southwest a wall of fog had advanced upon his ship. Great convolutions of vapours flew over, swirling about masts and funnel, which looked as if they were beginning to melt. Then they vanished.
This is a paragraph excerpted from a short story by Joseph Conrad: Tha Tale. At first glimpse, I thought it is a plain "so adjective as" comparison sentence. I, however, got lost where "that" popped up.
1) I cannot understand why there is "that" right after "as", and what its grammatical function is.
2) I wonder what this sentence means. Does this mean that the narrator(I) doesn't know that the commanding officer delved so deep into something as the commanding officer delved deep into his feelings?