The first battleship I've sunk so far on my U-boat is a US New Mexico class.
Was night time, s-w of Australia. I managed to position my U-boat in front of the line of approach of a large US-task force I held position while submerged. Waited for the destroyer at the lead to pass, thankfully without detection. The New Mexico ship was the first BB in the main column. I fired my 4 forward torpedoes, all hit.
It wasn't enough to sink her, she was on her side a like 2Ks. Then the escorts moved in. I manouvered myself to the limping BB on her 9 so that I would overtake her on her 11 o'clock and used one of my aft-torpedoes as a final blow. Succeeded. However first I it took like 10 minutes of traveling side-by-side with the BB before she slowed to 1k so I could overtake her and fire a clear aft-shot.
Then I had to travel south for like 2 hours with 3 destroyers on my back. Eventually gave up.
My biggest kill yet, and made me sweat trying to lose the DDs
