Now, fellers, submarine technology by the time 1941 came around allowed for underwater comms, but not by voice, only "keyed" entry, or telegraphy...
See
Communication with submarines, specifically the VLF section, and
Very low frequency, especially the Applications section. Also, remember that the game allows one, count 'em ONE ambient background sound file, so you cannot rotate among "deep water", "shallow water" and "surfaced" modes for that, although... there is the "Creaks" file sets...
- perhaps there is a way to skin this cat yet... an experiment is called for here. If you happen to see a mushroom cloud on the horizon, do not worry, it is not radiologic... it might be full of microbits, as well as assorted pieces of plastic and fibrous material...
... also, if CapnScurvy happens by, he'd laugh his backside off that no one has bothered to attempt to write down the Morse Code message... Happy Easter!