In 2014, Zhang saw a person build a submarine through a TV program, this inspired him to build one by himself. Despite his family's concerns over the cost and risk, Zhang insisted on building his own submarine.

Drawing on his practical experience with boats and handcrafting, Zhang spent about 5,000 yuan ($700) on materials. It took him six months to build his first submarine, which is 6 meters long, 1.2 meters high and weighs 2 tons. Although his first submarine suffered from sealing issues during submersion, the invention earned him a utility model patent.

This submarine earned Zhang a national utility model patent. The only fly in the ointment is that it leaks when submerged.