Hi again U-Cass
About the flags... yep, well, that's the problem with it being dark
About getting the range/aob... normally, just use the range/aob finder. On
really dark nights, bringing down the range/aob finder can make it impossible to actually see the target ship (because of the contrast between the two) so in those situations I suggest before lowering it you count vertical marks using the marking lines on the side of the scope, and only then lower the range/aob finder to calculate the range. If you know the convoy's course you can calculate the AOB from that - or, again, count marks using the lines on the scope.
Hope this helps
OLC