Sonar

1822 Daniel Colloden used an underwater bell to find the calculations of the speed of sound underwater in Switzerland.
1906 Lewis Nixon invented the first sonar type listening device to detect icebergs.
1915 Paul Langevin invented first device for submarines.
1918 Both Britain and the U.S. had active sonar systems.

Source: http://inventors.about.com/od/sstartinventions/a/sonar_history.htm

Active sonar sends a pulse of sound also known as a “ping” and then listens for the reflection. For long distances, the active sonar uses lower frequencies. The receivers measure the distance of an object by taking the time from emission of the pulse to the reception Courtesy of Wikepedia: Sonar Passive sonar listens without transmitting anything. This sonar is usually used for military purposes. The systems usually have large sonic database to identify classes of ships, actions, and particular ships.
Courtesy of Wikepedia: Sonar	A fish finder or a depth sounder is one of the simplest sonar devices. They send out a narrowly focused pulse. The information that it transmutes determines the distance and the objects density. These devices are used to locate fish, to determine sea-floor depth, and sea-floor composition.
	More sophisticated devices employ side-scan sonar. They are encased in a torpedo-shaped tube and are “towed” behind and below the boat. Everything in a 180-degree range is the field of view. The more sound pulses that are received from an object, the stronger they return, and the clearer the sound picture is. Usually rough surfaces return strong echoes while smooth surfaces return little energy. The side-scan sonar devices are very detailed, 3-D pictures of objects through computer analysis of the returning sound waves. These devices are used in many different ways such as to map features, including hills and valleys on the ocean floor, locating submarines, mines, and shipwrecks, and to inspect pipelines, cables, and bridge foundations.	Courtesy of Wikepedia: Side-scan sonar

• Passive transponders allow a computer to identify an object and must be used in conjunction with an active sensor to decode and transmit its data. They can be very small and their information can be detected at a distance of several feet. An example would be the magnetic strip on a credit card.
• Simple active transponders are used in location, identification, and navigation systems for commercial and private aircraft. With input and output frequencies determined beforehand, radio frequency transponders can be tracked and constantly monitored over distances of thousands of miles. Very sophisticated active transponders can operate on an interplanetry scale and are commonly used in communications satellites and on board space vehicles.