I recommend not being seen. Assuming you have radar, be at or below periscope depth when they come within 5 miles of your sun, on the way down to about 120 feet. It is possible they could see you down there, but sightings would be VERY rare. Hit the stopwatch when you pass periscope depth, pop back up to the surface at the 5 minute mark and there cannot be another airplane up there that you did not previously detect.
This eliminates the necessity of sitting at periscope depth, raising the air search radar antenna and looking around. You want to spend as close to 100% of your time on the surface as you can.
