Once the Second World War had begun with France and Britain as allies, German strategy aimed to win a short war in France and to force Britain to the negotiating table. After the conquest of France in May–June 1940, Churchill's refusal to surrender or to negotiate on terms favorable for Germany put the German gamble in jeopardy. Germany could not match Britain on the open sea and had not prepared its army for operations across the Channel. Instead, the Wehrmacht hoped to strangle Britain's economy through success in the Battle of the Atlantic (1939-1945) and the Battle of Britain (1940).