Sinking large ship using 2/3 deck gun shots

[Nuoz]

It is possible, under GWX 1.03, 100% realism. Only extremely difficult. I found that out on my last patrol. I spoted a large convoy. Calculated intercept course and all normal. It was a beautiful day, calm seas and clear as it can get. Guess i was really lucky that time (or not). First a frigates comes ahead. I don't know if it spotted my periscope as i was calculating speed and AoB (i didnt use the reported one because she seemed faster from the start) or it just heard me. I remember the plan was to let this frigate pass by, have a couple fish in the water to meet the larger ship and get out. I had plenty of depth so i was confortable. Well, to my surprise she starts pinging me! "OOpss you've messed up" i thought as i dived. Then i decided i wanted to be aggresive and try my luck. Periscope depth and i started running flank away from the frigate as it was persuing me. As she made 180º i lanched one magnetic triggered fish towards her. Bang, hit, she was going down. I noticed there was only Two more warships in the pack and one was a slow moving aux cruiser! I sank the other frigate pretty much the same way although this one tried to avoid my stern shot (i dived for the entire reload time changing speeds and depths always presuing the convoy (7knots) underwater) but failed. Then the aux cruiser. 2 Torpedos bang, she's dead. Now i have found myself ALOT of lone, unarmed (1940) merchants! Surface the boat! I was blowing 91 000 + tons on my first sight of enemies. The topic part now: If you point directly at the watermark (you must have a splash in the water) you can sink even the most powerful vessel easly. I've broke a large tanker in half with only 2 or 3 deck gun shots. On a side note, the way i cleared the opposition isnt really hard to do even in 100% realism as i did. That is wrong. For some reason they didn't fire at my periscope but once. I think there was a frigate and a much smaller warship i can't recall. Please comment.