The French Army put up a fierce resistance along the Seine and had some notable successes against the invading forces. Ultimately they had no answer to the German Blitzkrieg tactics which saw deep penetrating manoeuvres by the Panzers, which outflanked their defensive positions. Rommel was to lead his Division in a hundred kilometre drive forward in just two days. The Luftwaffe had by now almost complete air supremacy not just air superiority, giving them complete freedom to support the land forces.
On the 9th June the French Government learnt that German forces were just 50 miles from Paris. They prepared to join the mass exodus of the population themselves.
By this time British were recognising that the French cause was probably lost. Although further British troops were being sent to France and the idea of a Anglo-French redoubt in Britanny was being mooted, the realist in Churchill recognised that France was probably lost. On the 9th June he wrote a remarkably prophetic letter to his friend General Smuts, Prime Minister of South Africa:
Prime Minister to General Smuts
We are of course doing all we can both from the air and by sending divisions as fast as they can be equipped to France. It would be wrong to send the bulk of our fighters to this battle, and when it was lost, as is probable, be left with no means of carrying on the war.
I think we have a harder, longer, and more hopeful duty to perform. Advantages of resisting German air attack in this Island, where we can concentrate very powerful fighter strength, and hope to knock out four or five hostiles to one of ours, are far superior to fighting in France, where we are inevitably outnumbered and rarely exceed two to one ratio of I destruction, and where our aircraft are often destroyed at exposed aerodromes.
This battle does not turn on the score or so of fighter squadrons we could transport with their plant in the next month. Even if by using them up we held the enemy, Hitler could immediately throw his whole [air] strength against our undefended Island and destroy our means of future production by daylight attack.
The classical principles of war which you mention are in this case modified by the actual quantitative data. I see only one sure way through now, to wit, that Hitler should attack this country, and in so doing break his air weapon.
If this happens he will be left to face the winter with Europe writhing under his heel, and probably with the United States against him after the Presidential election is over.
Am most grateful to you for cable. Please always give me your counsel, my old and valiant friend.