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.
Diesel-electric submarines can last 2-3 weeks under water before resurfacing. Diesel/battery submarines do not dive very deep. These are quick attack sub's and often carry cruise missiles that they launch from just below the surface. There is special machinery on board that recycles and purifies the air.