Identify the parts of speech of the underlined words from the following paragraph. Submarines are ingenious bits of engineering designed to carry people safety through very harsh environment. Although they were originally invented as military machines, and most large subs are still built for the world's navies, a few smaller subs do work as scientific research vessels. In a floating submarine, the ballast tanks are mostly filled with air, just a small amount sits in the bottom. A submarine sinks when the tanks are open, electric pumps force air into the tanks, pushing the water out of the open holes.