P42 I think.
Thanks Vraciu. I can't see shore batteries on the map I have access too, but it does seem like for a breakout to be feasible, the overlooking bases need to be captured or the shore batteries neutralized before attempting to traverse a narrow passage.
Keep the comments and observations coming guys; I think they could help improve the design of subsequent terrains.
Maybe we have to reduce the number of shore batteries at choke points, or maybe this style of map requires greater coordination of effort between players? I'll be disappointed if breakouts turn out to be truly impossible though.