Plot hole: The factory in Norway has to be destroyed - at huge cost - as it is producing fuel for the V2 rocket. That fuel was ethanol - ordinary industrial alcohol. There is no reason at all to have a specialised factory hundreds of kilometers away producing such a simple chemical. The Germans could have manufactured it in virtually unlimited quantity in an ordinary brewery - and there were plenty of those in Germany.
Plot hole: Turgidson's 'secretary' listens to the incoming telephone messages for only a second or two, and relays a much longer message than she could have heard during that time.
Plot hole: In the beginning, Charlotte insists to Velma that cousin Miriam is coming, but Velma says "She's never answered any of your letters." And Drew says she's not coming. But when Miriam does come, only seconds later, Velma and Drew now act like they were expecting her. Velma says "You nearly beat your telegram. We weren't expecting you till tomorrow." It's like the film has been badly edited, with Miriam's announcement of her arrival ending up on the cutting room floor.