Wah?
The largest number of U-boats that attacked a convoy was 51 boats (some sources say 41) from four wolfpacks against ONS-5 in April 1943. Not a regular occurance mind you.
The 42-ship convoy was escorted by a destroyer, frigate and 4 corvettes.
The end result: 12 ships sunk...7 U-boats lost.
Hardly what I'd call the wreaking of havoc.
Methinks some people may need to read up on actual Wolfpacks.
http://uboat.net/ops/wolfpacks/ gives a nice summary of most (it's incomplete) of the wolfpacks including size and ships sunk. Some romanticists may find the stats surprising...