Submarines are special types of boats designed to travel underwater. They can dive deep into the ocean and stay submerged for long periods. Submarines are used by navies around the world, like the United States Navy, for military purposes, but they also play a role in scientific research and exploration of the ocean. Inside a submarine, there are living quarters, control rooms, and equipment to help the crew breathe and navigate. Submarines can be powered by nuclear energy or diesel engines, allowing them to travel great distances without needing to surface frequently. Their unique design helps them withstand the immense pressure of the deep sea.