Edgartown, its ears unconsciously expectant of the crash of bombs, had a thrilling experience Monday morning when the quiet June air was blasted by what sounded like nothing less than a fleet of bombing planes. The sky proving as blue, and benignant as it should on a proper June day in Edgartown, the population, or a large part of it, followed the sound to the harborfront, and was rewarded by the sight of a fleet of menacing looking mosquito boats.