usually I am very cautious about making positve ID before firing.
This time I was not.
What saved me from sinking the friendly neutral was that I noticed
that the crew did not cheer the hit as they usually do. 
...and this caught my attention in time to discover my error....and so halt the attack.
I am just glad that I did not launch the attack with a normal salvo of 2-3 torpedos.
As it was, I left the ship slowed to 2 knots and lisiting badly but managed to clear the area before I got "credit" (
) for the mistake.