What is a sub?

marine.

A submarine, or sub, is a watercraft that is designed to operate underwater. It is commonly used for naval warfare, scientific research, and exploration. Submarines are propelled by either nuclear power or diesel engines and use a variety of sensors to navigate and communicate. They are equipped with torpedoes, missiles, and other weapons for self-defense or offense. Submarines are typically crewed by highly trained personnel and many have the capability to stay underwater for months at a time. Maintenance and repair of a submarine require specialized skills due to the complex machinery and systems involved. Submarines have played a significant role in modern warfare, with numerous conflicts involving these underwater vessels.