Slitherine

A submerged sub is able to spot/identify an air unit. Persicope up!
The float-plane in the screenshot was revealed as I moved the sub two hexes south.
It was an UFO before the move.

Hm, afaik on periscope depth it would not be unrealistic per se...I mean you have usually several periscopes for targetting, observing etc., incl. one observation scope that can be used to watch the sky as well. of course, if it would be wise for subs to stick the scopes out when aircraft appear instead of diving deeper is another question.