Submarines have been conceived for many years, but only became practical in about 1900. Submarines have changed a lot in design from their first making which was in the years B.C. This sub was a box held under water with big ropes. New submarines are nuclear powered and can move at a speed of 30 knots and are big war weapons. The first submarine that could stay under water on it's own and move on it's …showed first 75 words of 468 total…

…showed last 75 words of 468 total…the ballast is empty, both holes close. When the sub comes above water, the air tank is filled so that the sub still has enough air in it's tank to surface the next time it wants to. Subs are the most complicated war tools and take a lot of hard work and money to make and keep operational. But when subs are finally made and ready to attack, they are a devastating weapon of war.