I was playing DiD the other week, on my 11th patrol heading for home, and I didn't zoom the map in enough to see that my plotted course went straight through a small island NW of Scapa flow. At least that's what I think my mistake was, on high TC my IIa got destroyed (a mine maybe?). If I'd made it home I would have had a brand new VIIB waiting for me.......
Maybe I'll reload that one. Not sure.