During 1990â2003, Pakistan sustained its historical lead as the second-most urbanized nation in South Asia with city dwellers making up 36% of its population. Furthermore, 50% of Pakistanis now reside in towns of 5,000 people or more.
Submarine Propulsion Systems. During World War II, most American submarines were powered by diesel-electric systems. This was a departure from earlier submarine power systems, which were direct drive types, little changed from the earliest boats. In this direct-drive power system, the diesel engine is directly connected to the propeller shaft.
Sonar can be categorized as being active or passive. Active sonar involves the transmission and reception of sound waves. For example, when a submarine is used to map the topography of the ocean's floor, it sends out sound pulses, often referred to as pings, towards the bottom of the ocean within its vicinity.