Off the main thread topic: Anyone making those arguments doesn't know a thing about WWI and WWII submarine history then. The majority of kills were made with the deck guns, including large cargo ships and tankers.
For documentary evidence, the easiest place to look at for the U-boats is http://www.uboat.net/.
The record holder for any side in any war ever is Kptlt. Lothar von Arnauld de la Perière in WWI, with 195 ships sunk or captured (459.679 tons) and 7 ships damaged (31.810 tons) - almost all with deck guns.
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