Ultrasonics was conceived and came into being in France in a wartime academic atmosphere. Its physical principles were explored in England and in this country during World War I. Piezoelectric quartz was the primary, and for many years the only, active transducer element which was utilized in Europe. However, as soon as the work was started in this country, vigorous innovations were introduced. Synthetic Rochelle salt crystals were investigated and applied. Some theoretical work and several experimental techniques were developed in the United States concerning transducers. Of the number of outstanding physicists identified with this effort in America, most returned to their universities as soon as the emergency was over, and the subject of ultrasonics become dormant during the twenties. The Navy maintained an interest in ultrasonics and sponsored classified projects in the field. The subject of piezoelectricity was advanced, new synthetic crystals were brought forth, and large-scale processing, cutting, grinding, and lapping of crystals were started and pursued by the Navy. An American version of the steel sandwich was produced for operational tests. The Pierce magnetostrictive devices were incorporated in sonar systems. Similarly, the electrodynamic principle was implemented into a useful transducer. A variety of absolute and secondary standards were developed.