Sonar

Sonar (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR (an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

Das Boot

Das Boot (German pronunciation: [das ˈboːt], German meaning "The Boat") is a 1981 German epic war film written and directed by Wolfgang Petersen, produced by Günter Rohrbach, and starring Jürgen Prochnow, Herbert Grönemeyer and Klaus Wennemann. It has been exhibited both as a theatrical release and as a TV miniseries, and in several different home video versions of various running times.

Das Boot is an adaptation of the 1973 German novel of the same name by Lothar-Günther Buchheim. Set during World War II, the film tells the fictional story of U-96 and its crew. It depicts both the excitement of battle and the tedium of the fruitless hunt, and shows the men serving aboard U-boats as ordinary individuals with a desire to do their best for their comrades and their country. The screenplay used an amalgamation of exploits from the real U-96, a Type VIIC-class U-boat.

Development for Das Boot began in 1979. Several American directors were considered three years earlier before the film was shelved. During the film's production, Heinrich Lehmann-Willenbrock, the captain of the real U-96 and one of Germany's top U-boat "tonnage aces" during the war, and Hans-Joachim Krug, former first officer on U-219, served as consultants. One of Petersen's goals was to guide the audience through "a journey to the edge of the mind" (the film's German tagline Eine Reise ans Ende des Verstandes), showing "what war is all about".