The IX boats were hampered by being much slower diving than the VII's. This becomes a factor when operating close to coasts early in the war and later on when there was pervasive ASW patrols via escort carriers and long range ASW aircraft later on.Sure. I think the performance of the uboatwaffe would've been improved, and its effectiveness prolonged, perhaps considerably, if three changes were made. First, emphasize Type IX construction. Considering that the bulk of sinkings and the most remunerative patrols occurred in remote, peripheral areas, the Germans should've invested more in long range boats. Second the IXs should not have been used in anti-convoy operations, not even on their first patrols when coming out of the Baltic. Third, they should've maintained absolute radio silence, save for emergencies, when transiting to or from patrol areas.
Well, even if the Germans emphasized long range boats they still had to attack convoys, at least occasionally, with the VIIs they had so the allies had to maintain the convoy system, to the detriment of efficient shipping circulation.