My interpretation about the soon-to-be added G&B map:
Bri'ish diplomat who was in the town of roscoff for peacetalks with the french due to the ongoing apocalypse sends out a distress letter due to the town getting overrun, killing jean in the process, then, after the letter is received, American marines [also 1st infantry or whatever its called] and some bri'ish units get sent to roscoff per ship to assess the situation and get the diplomat out
They find the town in shambles, left only the stench of the rotten, walking corpses roaming this once peaceful town.











