I detected a Polish merchant but was going to just continue on to Kiel. The problem was, heavy fog. I didn't feel like dealing with the frustration of not being able to get eyes on and he was already moving away according to my hydrophone man. I decided "What the hell!?", let's put that practice to the test.
I re-submerged, re-acquired the contact, and proceeded to use the first 3 bearings of the 4-bearings method so that I could determine his course. He was moving away, so I didn't want to take the time to relocate to get the 4th for cross bearing and with only 5 minute intervals I would've been really pressed. I determined his course, had his speed estimated as slow so I chose 7 knots as target speed, and used the Attack Disk to get a 10 knot intercept. Surfaced and ran towards with no more excursions below to check whether he changed course.
Ran it at 1x TC since I didn't know what his distance was, and didn't want to risk missing the contact.
40 minutes later, appearing rather largely out of the fog, the deck gun crew got some target practice, and we all got some tonnage.
Glorious!