The following is a short summary of the circumstances leading up to the Battle of Britain between May 1940 and the end of June 1940. This was the period during which the military, strategic, and territorial balance in Europe was profoundly altered by German victories.
When the Second World War began in September 1939 there was little prospect of the Battle of Britain ever being fought in the first place. The Germans had quickly defeated Poland yet seemed to be roughly equal in strength to the British and the French.
The disastrous Anglo-French campaign in Norway led to the replacement of Neville Chamberlain with Winston Churchill as Prime Minister on the very day, 10 May 1940 that the Germans launched their offensive against France and the Low Countries. As the defeat of France became inevitable the qualities of Winston Churchill in keeping Britain fighting alone came to the fore. Churchill perhaps more than any other person kept trying to persuade President Roosevelt to change American policy towards Britain and to a great extent succeeded (Parker, 1989, pp.44-45).
With Churchill as Prime Minister the remote prospects of Britain making a deal with Germany diminished further. The Roosevelt administration were concerned that if Britain was defeated or forced into a peace deal that the most powerful ships of the Royal Navy could be used by Germany or Japan and pose a significant danger to American economic and military interests. For Roosevelt and the United States as a whole the consequences of Britain’s defeat could have been catastrophic. It was in Roosevelt’s best interests to keep Britain in the war and prevent outright German victory. Britain’s lonely fight was portrayed as the stand of liberal democracy against Nazi tyranny (Townshend, 2005, p.142). American military and naval experts regarded Britain’s survival as strategically vital for the effective defence of the United States itself. Britain was also seen as a strategic stepping stone for liberating Western Europe from German occupation should the American government decide it wanted to intervene to do so (Hobsbawm, 1994 p. 39).
Britain’s determination to survive was shown even before the Battle of Britain by the Royal Navy action at Oran to prevent French ships being used by the German navy. Although Churchill had not found the decision to attack a former ally easy he had been prepared to make such a decision to ensure Britain’s survival. Roosevelt could therefore contemplate increasing support for Britain as it had a government that was ruthless and determined in fighting on when many governments in similar circumstances would have sued for peace (Kennedy, 1976, p.301). Churchill had ordered that the French navy be neutralised at all cost (Churchill, 1948, II p 205) Oran persuaded Roosevelt that Britain was worth supporting as much as any of Churchill speeches or letters could have done. Churchill went out of his way to forge strong relations with Roosevelt as gaining American support was the key not only to survival yet eventual victory as well. Churchill regarded an Anglo-American alliance as the only means of defeating the Axis powers whose aggressive policies would ensure that the United States would have to fight eventually. American isolation was as unrealistic as Anglo-French appeasement policies had been at averting war (Jenkins, 2001, p.624).
After the defeat of France the British Army was in a bad state and would have little prospect of defeating a German invasion force if it had landed. Without the successful evacuation from Dunkirk the situation would have been worse. All that stood between survival and defeat was the Royal Navy and the RAF. The Royal Navy had large numbers of ships that could be used to repel German invasion forces yet had to take them off convoy escort duties and thus increasing the strain on Britain vital supplies (Deighton, 1980, pp. 85-86). Churchill’s speeches in the summer of 1940 were not only used to rouse the defence of Britain they were used to gain support from the American government and the American people. Churchill appealed to the United States for help as together Britain and the United States could overcome the Axis powers and restore democracy and freedom to Europe. The White House and Roosevelt believed that the threat of Germany’s invasion of Britain in June 1940 was real enough to contemplate offering Britain assistance (Colvin, 2003, pp.262-3). From the start of his premier-ship Churchill decided that it was in Britain’s best interests to keep Roosevelt informed of Britain’s military and naval weaknesses to gain support whilst assuring Roosevelt that Britain would survive and not waste that support (Stafford, 1999, pp.6-7).