Early in April the British and German pressure on Norway converged. On 8th April the British arrogantly disregarded the neutrality of Norway and mined its waters; on 9th April Operation Weser River Exercise was launched upon the discovery of a British invasion force. The subsequent British failure in Norway caused the fall of the Chamberlain government. Meanwhile, Hitler launched his attack in the west, prompted partly by this dark example of ruthless British arrogance and brutality towards neutral countries. On 10th May Winston Churchill became Prime Minister of Britain while the Germans were invading Belgium and Holland. Directives 11-15 deal with the series of battles in the west which led to the evacuation of Paris on 14th June and the formation, two days later, of the government of Marshal Pétain, which surrendered to Germany.