Are submerged/periscope attacks too easy?

I got started thinking about this from another thread, where it was mentioned that the tonnage people sink seem unrealistically high when compared to actual wartime statistics. That got me thinking about how I conduct my attacks versus what (little it may be) I know about historical U-boat attacks.

Virtually any convoy attack I make, day or night, is a submerged one. It's only if I play very early in the war that I make night-time surface attacks on convoys. Singletons or doubletons I might still attack on the surface (at least until they start getting armed! :p ) but usually my periscope gets a workout.

However, from what I've read it seems that the majority of attacks, even against convoys, was conducted on the surface. I recall reading one account (from the Allies perspective; I wish I could remember where I read it at ) where they said that, over hours thru the night the individual subs of the attacking wolf pack would surface some distance out, then dive as an escort charged toward them, only to re-surface again and again trying to get in an attack.

I don't understand why they didn't remain submerged and try creeping in for an approach while submerged. Part of the explanation was the very slow speed the boats had while submerged, which made it difficult to adjust course and close the range. But I don't seem to have trouble doing that in-game, which is why I wonder if it's far easier to conduct a submerged attack in SHIII than it actually was. And, if that's true, if there's any way of making a submerged attack more historically accurate and reflect that difficulty.