A submarine is a watercraft designed to operate underwater. It can travel deep beneath the ocean's surface and is used for various purposes, including military operations, research, and exploration. Submarines are equipped with advanced technology that allows them to navigate and communicate while submerged. Most submarines are powered by nuclear or diesel engines, enabling them to stay underwater for extended periods. They are often used by navies around the world, such as the United States Navy, for stealth missions and surveillance. Additionally, some submarines are designed for scientific research, helping to study marine life and underwater ecosystems.