I'm learning about the capabilities of German u-boats during the Battle of the Atlantic and their improvements during the war, in the most general sense.
I researched three types of U-boat, the VIIA, VIIC, VIIC/41. (Source)
Top speed: approx. 18 knots on surface, 8 while submerged. This doesn't appear to have improved much during the war.
Range: approx. 6000 miles (at 10 knots) with the earlier VIIA, but 8500 miles with the later versions. A further improvement (the VIIC/42) was planned that could travel more than 12,000 miles, but none were built.
Armament: Early models carried 11 torpedoes, later ones carried 14. Most had some smaller arms on the deck for use on the surface only.
Torpedoes: The T1 was flawed due to its visible surface bubbles but had a fairly large range and high speed (6000m at 44 knots). Later models like the T2 and T5 had a lesser range (5000-6000m) and speed (20-24 knots) but improvements in their ability to seek loud objects and better detonators. There were 4 bow tubes and 1 in the stern. (Source)
Passive Sonar: A slow-moving u-boat (4 knots) could hear a cargo ship from 3.5-7.5 mi. away, a destroyer from 5-10 mi. away, and a large convoy up to 50 mi. away. As the u-boat increased its speed, its listening range was reduced significantly. (Source)
Radar: U-boats were fitted with radar for the active detection of ships (while surfaced), but they were either ineffective or seldom-used because of the chance of giving away their own position. (Source)
Have I grossly misunderstood any of this, or is my summary of the capabilities of German u-boats sufficient as a starting-point? Are there other, more important, capabilities that I have neglected to learn about?