Read the paragraph.

A submarine is a type of naval ship. The submarine was first used in combat in 1776 against the British during the American Revolution. The submarine was called the Turtle. It was an American ship and it was invented by David Bushnell, a student at Yale University. The Turtle was made of wood, it was oval and it looked like an egg.

Adapted. Campaign. English for the Military. 2004. Macmillan.

According to the paragraph, the machine was