The undulatory progress of wind wave research in the past two decades is chronologically summarized by the following quotations:
The present state of our knowledge is profoundly unsatisfactory [Ursell, 1956].
The three elements needed for determining the mechanisms of water wave generation by wind … were shown in a review by Ursell  to be all wanting, but in that by Longuet-Higgens  to have been in. large measure supplied in the intervening six years [Lighthill, 1962].
After a decade of intense study, which has seen the development of numerous wave generation theories … it is now evident that the mechanisms mainly responsible for the most rapid stage of growth of sea waves under the action of the wind still remain to be found [Longuet-Higgins, 1969] (introduction to a paper presenting yet another mechanism of wave generation).