Use of Sonar in Harbor defense and amphibious landing operations

During World War II, harbors were guarded against sneak attacks by enemy submarines by a device known as Herald. To install, operate, and maintain equipment sufficiently simple for use at frontier bases required considerable development, including such engineering problems as submerged installations, remote controls, and operating adjustments. Ultrasonic devices also were developed, for use in establishing beachheads under darkness, each unit of which contained its own power device and method of self-destruction.