Bombing Raids on Our Cities. In attempting to bomb one of our great coastal cities such as New York or San Francisco, the enemy would not be likely to use heavy demolition bombs. This does not seem practical because of the great distances which would have to be flown to and from the objective, and the limited number of such bombs that can be carried even by the largest type of bombing plane in use today. It is the belief of military experts that any attack on our great cities would be more in the nature of a "token" assault. The chief object of such a bombing foray would be not so much to cause really thorough and widespread destruction as to disrupt the normal industrial routine, to create fear and panic, and in general to undermine the morale of the populace. For such "token" bombings, the enemy would be likely to use some fragmentation bombs, together with a large number of small and mekium sized demolition bombs, and above all, veritable showers of fire-producing chemicals.
The above way of thinking was overshadowed for a long time by the development of atomic bombs and hydrogen bombs, and by the later development and deployment of ICBM missiles that could deliver them directly and quickly. But with the end of the Cold War and a stand-down of the mutual ICBM threat, this 1943 paragraph has new relevance when you view it in light of the 9/11 attack on New York. What wasn't forseen was that such a "token" assault would be carried out not by an enemy's bombs or bombers, but by the enemy's innovative use of our own civilian airplanes, filled to the brim with those "fire-producing chemicals".
Moral: Don't dismiss old wisdom without re-evaluating its relevance in a changing world. That's one reason we teach history.