[DeepSix]

I've always thought the game doesn't give the player an accurate operational range at Standard speed, but I don't know for sure.

Along the same lines as other posts - best to cruise on the surface at 2/3rds (12 knots on a calm sea). Aircraft may force you to dive; click the tab below the telegraph dial and then set your speed to 2 knots. At that speed, you can stay submerged all day and surface again after dark (about an hour after sundown is good).

One other suggestion - don't chase after every contact you get while enroute to your patrol station, especially if they are on a diverging course (moving away from your direction of travel) or at extreme distance. Probably better to let it go because there will be others. Targets on a converging course, though....