Newbie problem with torpedos

[herrkapitan]

I am new to SH3, but love the game.
I am doing a career, finished 4 patrols.

On my 5th patrol I ran across a C2 Cargo and I setup a silent/perfect trap. I used automatic targeting and once the ship was about 180-200 m I launched my torpedo after it was 'green' in the periscope view.

The torpedo 'missed'? How did that happen?

So I come around, setup another shot and launch another torpedo with the C2 Cargo dead ahead of me. Missed again!!! I was about 150 m from the ship.

Now what am I doing wrong? Am I too close? What is the minimum range for a torpedo to be armed?

Or is my depth in correct? I tried changing it in TDC to be about 3 m from 4 m default and it made no difference.

Any help would be appreciated as I am pulling my hair out.