Zhang Shengwu, a 51-year-old farmer from the Chinese city of Maanshan, built a stunning invention - his own personal submarine! Made out of metal and welded by hand, the 20 foot long and 2 foot wide home-made vessel can only travel up to seven nautical miles per hour and dive to a depth of about three feet, but, it only cost Zhang about $760 to build, and, to top off this incredible feat, he finished building the sub in two months.