Are submerged/periscope attacks too easy?

[Sailor Steve]

As mookiemookie said, night attacks pretty much had to be done on the surface as periscopes don't allow enough light to be useful unless a full moon is out. Daylight attacks must be made submerged (or you're dead), which means risking staying surfaced long enough to do an end-around to get in front of the convoy and dive again.