On 5th August Churchill had sent a memorandum to the Chiefs of Staff on his strategy for meeting a possible invasion. He believed that the first three lines of defence were:
i. monitoring the enemy ports and attacking any build up of shipping
ii. ‘vigilant sea patrolling’ to intercept any invasion expedition and ‘destroy it in transit’, and
iii. ‘counter-attack upon the enemy when he makes any landfall, and particularly while he is engaged in the act of landing’.
He saw that the Royal Navy and RAF would have the principal role in forestalling any invasion …
However, should the enemy succeed in landing at various points, he should be made to suffer as much as possible by local resistance on the beaches, combined with the aforesaid attack from the sea and the air. This forces him to use up his ammunition, and confines him to a limited area.
The defence of any part of the coast must be measured not by the forces on the coast, but by the number of hours within which strong counter-attacks by mobile troops can be brought to bear upon the landing places.
Such attacks should be hurled with the utmost speed and fury upon the enemy at his weakest moment, which is not, as is sometimes suggested, when actually getting out of his boats, but when sprawled upon the shore with his communications cut and his supplies running short.
It ought to be possible to concentrate 10,000 men fully equipped within six hours, and 20,000 men within twelve hours, upon any point where a serious lodgment has been effected. The withholding of the reserves until the full gravity of the attack is known is a nice problem for the Home Command.
On 17th August Churchill received a memorandum in reply from the Chiefs of Staffs Committee, in which they stated they were in ‘complete agreement’ with these general principles, and outlined the disposition of the 26 Divisions that were available to provide the mobile reserve. It was only now that he distributed these two memoranda to the rest of the War Cabinet. Churchill was both Prime Minister and Minister for Defence and had streamlined the decision making process, although his memoranda and directives were not always met with full agreement by the Chiefs of Staff.
See TNA cab/66/10/50
The troops based on the coast were stretched very thinly, as can be seen from 2nd/4th South Lancashire Regiment War Diary.
Churchill was sceptical about the prospects for a successful invasion, which he had assessed on the 10th July 1940.
It was a perspective that he carried over when the situation was later reversed, when the Allies were considering an invasion of France. Churchill was to lead opposition to proposals from the United States for the Allies to land in Europe in 1943. When D-Day was launched in 1944 the “nice problem” of “withholding of the reserves until the full gravity of the attack is known” was faced by Hitler – a problem that the Allies managed to greatly exacerbate with their elaborate deception plans.