America's "European allies were brought along to acquiesce in the United States engaging in the rational activity of discovering whether there was after all some defence against nuclear attack ... by the apparent assurance obtained from the United States that it was only engaged in experiment and research, and that, if there were any danger of effective protection being devised, of course the United States would not avail itself of that protection without the agreement of its European allies. That was the first recent event which shook to its foundations the nuclear deterrent with which we had lived these last 30 years".