[Major Johnson]

I would say that in real life the weather plays a big part of this equation. On a clear day and calm seas, I wouldn't be surprised to hear that a sub is visible down to 100 ft. In bad weather, ie, rain, chances are there's not going to be planes flying anyway. Another point was made about how high the plane is flying. Another good point, but for the sake of this game, I would say every plane is flying at a height normal for looking for subs. No point in having high level bombers. Also the cruising speed of most sub hunting planes wasn't 300 mph, it was normally around 200 or below. The 300 mph range is normally getting close to the top speed of the craft flying level. I recall seeing photographs of Uboats that were under the surface, taken by our own WW2 anti sub patrols. Many of those were taken by slow/low flying blimps, but there were also personal craft used for ASW as well. So I have no problem with planes being able to see a sub at periscope depth during ideal conditions.

On a side note, wasn't the Union ironclad "Monitor" found by a plane?? And I believe it was in 100 ft or so of water.