Contact Reports
 

Am I supposed to send them on detecting a contact, or after sinking it? I only wonder because I've never received any acknowledgement when I've sent a report (not even a 'be more aggressive'), and sending a transmission whilst stalking a target doesn't seem that bright.

No, SUBCOM is very quiet on your successes but sure as heck send more contacts for you.

Do know that sending messages might give your position away, atleast according to this command:
Enemy Air Strike Probability Increase on Radio Messages Sent=30 ;[>0] Increase over the default probability on a radio message sent

But there's hope:ping::
Friendly Air Strike Probability Increase on Contact Report Sent=70 ;[>0] Increase over the default probability on a contact message sent

If you report a convoy or task force you will sometimes get a mission objective to sink some ships which I'm assuming is worth extra renown.

Cheers, thanks.