Many thanks, gents!
Am playing unmodded (except for adding a Gato sonar bearing fix) v1.5 from the Uboat add-on CD. I want to gain more familiarity with the platform before venturing too far into "mod land".
I have "shelled out" to Win 10 off and on, and that discussion makes sense.
I discovered the exit and return CO2 "fix" by happenstance.
The red symbols are all square or diamond "targets in waiting", ships, convoys, task forces. I also save games frequently and start my sessions from a saved game... Will do some experimenting to see if that's the culprit
http://s244.photobucket.com/user/jim...rgets.jpg.html