General Sir Edmund Ironside, formerly Chief of the Imperial General Staff, was now Chief in Command Home Defence, responsible for preparing the response to any invasion. His diary shows that he believed that an attack could come at any time, but that intensive air attack was likely to come first:
It is curious how one goes to bed wondering whether there will be an attack early the next morning. As we have done all we can in the way of preparation, it doesn’t worry me much. I merely give thanks that we have another day of preparation and issue of defence material.
The attack upon us by air is intensifying. Chiefly against aerodromes, ports, shipping and aircraft factories. But so far the attack has been badly directed and not carried out in great strength. The R.A.F. say that that is what happened before the German attack in France. Desultory bombing and then one morning a very heavy attack on everything. It may be coming again. The seemingly desultory bombing may be a method of testing our defences. Certainly the Germans have never been up against such a good fighter defence, such A.A. fire, and such a warning system.
I am inclined to think that Germany will try to wear down our air defence before she tries any invasion. It seems the natural thing to do. . . .