I like the Type IX, use it a lot, but it is a real slow pig when crash diving. Has a clunky feel to it.
It seems that you could send your kid off to Kindergarten and get to 20 meters by the time they graduate college.
To help with the diving time, I run with decks awash when conditions permit, It shaves off a few seconds so. I don't like using radar, I feel it is more of a attract-er for trouble, but I feel it evens things up game wise with aircraft if visual sighting is utilized. As John said, the aircraft can be inaccurate when dropping bombs.
It is great for hunting single merchantmen or off the coast of USA for tankers and the Kapstadt Kampaign in the South Atlantic.
Good hunting,
FUBAR295