How to use sonar properly?

[Paul Riley]

During my previous engagement with the huge convoy I mentioned in my recent posts,I mentioned that I hit a T.Transport earlier and it fell behind the convoy.I then decided to break off from the convoy and re-aqquire the Transport,which I did.I picked up a hydrophone contact and proceeded to advance towards it.I set the u-boat up on roughly a 90 degree track alongside the Transport,to fire a 90 degree shot.It was very dark and visual contact was made at about 4000m if I remember,and I went to PD and closed the gap to about 3000m,my firing range.At this point I wanted to use my sonar,so I could track the final moments without using the PS.At this point I expected the sonarman to start using the sonar and start pinging him,which of course he did'nt.I went to his station personally and asked him to find target bearing,range etc,and he replied with "no target selected".I couldn't work out why the sonar was'nt working.Finally,I just stuck with my usual methods of engagement,and carried on alongside him tracking him with the PS and fired 2 perfect shots when he was at 90 degrees in the scope.
Can anyone explain to me why the sonar wasnt working,and under what optimal conditions the sonar should and should'nt be used?.
For the record,it is the first sonar model,and may explain some of its shortcomings
Does sonar become more of a neccessity as revealing one's position becomes more hazardous?.
NOTE: I must mention that it was my first real at chance using the sonar,as it was first fitted at the beginning of that patrol

Thanks for any advice