Slitherine

I'm at a loss on how to attack u-boats. When I spot a u-boat, which has attacked one of my allied vessels last turn, I move either BBs or DDs next to it or move a CV in range, but I can't seem to attack it, no white circle appears over the u-boat. Does weather have an effect?

Sub rules have changed in Grand Strategy. You can only attack subs before you move your units. So you should escort your convoys physically and then subs adjacent to the escorts after attacking can be attacked. Strategic bombers are also great due to their long range. They can be stationed in key locations like the Azores, Greenland and Iceland and reach attacking subs. CV's can also attack before they move, but the range is short until you get better air techs (strategic operations). Usually I put the CV in the center of the escorts so if the sub attacks one of the escorts or the convoy then the CV can retaliate.

Ah yes I was much too hasty, as Treebeard would say. I read the GS manual at it was obvious then. I see now why convoys that have only two escorts have one stationed fore and aft, so at least one can attack any sub that attacks the convoy in the previous turn.