Submarines are watercraft designed to operate underwater. They are used by navies around the world for various purposes, including surveillance, reconnaissance, and combat. Submarines can be powered by diesel engines or nuclear reactors, allowing them to stay submerged for extended periods. Their ability to remain hidden underwater makes them valuable for military operations. In addition to military use, submarines also play a role in scientific research. They can explore the ocean's depths, studying marine life and underwater geology. Some submarines are equipped with advanced technology, such as sonar systems, to help navigate and gather data about the underwater environment.