Patrol South of Ireland ( Carrier Hunt ) no joy in marked area, so I just plotted a search pattern and way I went , nice single merchant came into view. As it was night and as the rain was heavy it did see me sitting waiting for it, I fired 2 torps 1st hit front mast area the 2nd hit just aft of midships.
It did not go down I had 1 torp left a stern 1 and it was loading as I got a shout from sonar that 2 warships were closing _ distance - long so I sent off in the direction the Mercant was bound. 4-5 hrs later sitting waiting along it came

doing 10knts in a heavy sea with 2 large holes in her port side.
I had time to line up my stern , so I went down to pscope depth and waited, I don't know why but I hit the sonar button and got a
NO CONTACTS reply
BUG
I went below to see for myself ,
I sat in and turned the dial and sure enough I got the CONTACT I went back to the attack scope and hit the button again just to check and again the reply came back
NO CONTACTS.
I had her in my sights in the Attack scope and fired my last torp from the stern into her Starboard side midships and that finished her.
I am reading Battle of The Atlantic just now and most captains or there war diaries say 1 torp did most ships. One 7000tn Merchant
Kretschmer hit in a convoy attack was hit with 1 torp and in his diary says that one went down in 40 seconds. Another one he hit again with 1 torp a merchant seaman on another ship says in the book it went up in flames it was carrying sulphur and the flames were burning Green!
Same attack (wolf pack) he says that the Escorts were firing Star Shell but they were of no or little use in a moon lit night. Of that attack in the book BOTA a british sailor was describing his utter dejection about the DD he was on, could hardly do anything for the convoy stating that the Uboat on the surface at night were very hard to spot. Also said about the 4ins guns being not very good as well as only being able to lower them so far that even using them was of little use as shots would fly over and beyond the uboat(s). It was like hunting for a needle in a haystack because the ASDIC hopeless , a better hope and more chance was one of the wolf pack subs torp(s) missing its target and hitting another uboat.