This 4.5in sub is powered by baking powder. Powered by baking powder (not baking soda), it dives and surfaces just like a real submarine. As the baking powder reacts with the water, carbon dioxide is produced. This gas forces water out of the submarine decreasing its density and allowing it to surface. This is much the same way a real sub surfaces by purging its ballast tanks. After the sub reaches the surface, the gas bubble is allowed to escape, water takes its place, and the sub dives again. Approximately 11.4 cm (4.5") long and wonderfully detailed, this is a great science toy for discussing buoyancy, density and the production of CO2.