its unfortunate that you are going to unload the game.
Each convoy or ship you approach you must be secret and silent especially when DD's are involved.
As for the messages recieved, you as captain have to make a choice if you can or get the opportunity to grab some tonnage safely and aggresively; so you can bring your crew back to thier families.
Im always coming up on capitol ship and especially freighter convoys. I creep in at 1-2 knots rigged for silent running. taking my time and easing my way in to let loose a few fish to sink some tonnage. Get in thier, launch your sortie of fish and dip deep below the thermal layer and creep out alive to fight another day. Miss a ship or two? That's okay, go back out there for more.
Dont give up so easily, give it a another try.
Submarines are a "Silent Service."
Ahoooooga!
