Blekinge-class submarine

A Blekinge-class submarine is a kind of boat (or ship) that can go underwater. It's like a regular boat, but it has a special envelope, or "hull," around it that can keep in air and block out water. Inside the hull, it has very powerful engines that help it move through the water, and it also has special devices to help it go up and down through the water. It also has big, heavy batteries, so it can stay underwater for very long periods of time. They're usually used by countries to explore the sea, look for enemies, and perform military missions.