Just when I thought I'd run out of noob questions...
I have not yet tempted fate in this way, but someone must know: Can aircraft see your hull through the water at periscope depth on a sunny day (and attack you)? Even if we don't have SH4's transparent water, perhaps the visibility is modeled for the aircraft lookouts.
I reckon even before radar they
can see the periscope, or rather its wake, so I generally raise it only at slow speeds, and very briefly.
Vielen Dank!