I'll take a stab at this.

The 'average' range for attack was on the order of 1000 - 2000 m. A 'real' number could be made by analysis of attack reports, etc, but it gets a bit uncertain, since most attacks did not estimate distance to target well (the tendency was to think the target was farther - and bigger - than it really was).

Shots longer than a few thousand meters were extremely rare and even less likely to hit - the chances of hitting a fleeting object were just too small. It would be extremely rare to take a shot, and even rarer to hit, at over 4000 m. No one could aim and hit a target at the extremes of the ranges the torpedoes were capable of travelling.

I'm sure someone somewhere has a number for the longest range hit by a U-boat - someone got lucky with a long shot somewhere.

The longest documented hit by a submarine in any war was the 'lucky shot' by the Japanese sub I-19 that went past its intended target and unintentionally hit the USS BB North Carolina - at a range of 22,000 m. The I-19 also sank one carrier and damaged another - the most successfull salvo of any sub in any war.


Kurt