RW/Nef - thanks for that - I was able to survive by diving to PD and running silent. The only problem was that after a prolonged night time attack on a convoy, my batteries were getting low just as dawn came around. I had to shut down engines and give the crew a day off while we waited for night. It's summer time, and around the inner Hebrides off Scotland, it doesn't get dark till 11pm, and starts getting light again not long after 3am, so there's not much opportunity for recharging the batteries. And after the attack on the convoy I only had 3 torps left, so I RTBed to start another patrol...
...and in that patrol, at x1024 TC on the open waters, I ran into a Clemson which was attacking from a range of more than 2000 metres. I took some damage, but was able to dive to PD, and turn away from the Clemson. It very kindly kept a constant speed and bearing, and I was able to whack it with the stern torp.
I wasn't so lucky the next time. Still on the open seas at x1024 TC, I ran into another DD. By the time the warning came, the DD was already at p***ing distance, my VIIc having suffered catastrophic damage and flooding, and I was soon dead. The issue here is that this would not have happened in x1 TC - my guys would have spotted the DD and/or the sonar man would have detected it. The game does automatically change into x1 from x1024, but in many cases it happens much too late to be of any use. Sitting there at x1 for days at a time while my sub trundles to the assigned sector is not an option, so I think I'll do saves every 2 mins at x1024, and if this situation arises again, just go back to the last save.
I'm just about to download RUB 1.44 to see if this issue has been addressed.
