In the quiet countryside of Anhui Province, China, a 60-year-old farmer has defied expectations. With scrap metal, repurposed components, and unwavering resolve, Zhang Shengwu has designed and built a functioning two-person submarine that successfully submerged beneath a nearby river. First highlighted by China Daily, his feat quickly captured significant attention on Chinese social platforms, drawing both admiration and safety concerns.
Known as the Big Black Fish, this homemade craft can dive to depths of 8 meters and move at speeds up to 4 knots. Despite lacking formal education in naval engineering, Zhang has dedicated more than ten years to bringing this vision to life.
His journey began in 2014 when a TV program showcasing submarine dives ignited his curiosity. Having only witnessed cargo boats on the Yangtze River, Zhang found the concept of underwater travel mesmerizing. “I was used to seeing boats on the water,” he shared with SCMP, “but never one that could vanish beneath the surface.”
From Leaky Prototype to Online Sensation
Starting with just ¥5,000 (approximately $700) and a vision, Zhang's initial submarine was a rudimentary steel frame, hastily welded after long workdays. Though it leaked and barely submerged, lacking steering controls, it proved the concept could work. In 2016, this design earned him a national utility model patent, recognizing his pioneering effort.
This breakthrough boosted Zhang’s confidence, leading to the development of a second, improved prototype starting in 2023. Finished by mid-2025, this version spans 7 meters in length and weighs 5 tons, fortified by two tons of concrete embedded in the hull for better stability underwater. It features two ballast tanks to manage its depth, filling with water to sink and emptying to surface. Additionally, Zhang equipped the submersible with a waterproof riverbed camera mounted on a 5-meter pole to detect underwater obstacles.
One of its test dives even recovered a fisherman’s lost net, a small but meaningful victory that earned Zhang a ¥3,000 reward and further enhanced the vessel’s reputation.
Viral Success Meets Expert Skepticism
Videos documenting the submersible’s inaugural dive appeared on Douyin (China’s TikTok), showing the heavy steel craft smoothly disappearing beneath the murky water of the Fengle River before resurfacing moments later. The footage quickly amassed hundreds of thousands of views, with viewers praising Zhang as a contemporary inventor of genius.
However, some professionals remain cautious. Without formal safety certifications, experts warn homemade submersibles lacking specialized pressurised hulls and emergency ascent systems can be extremely dangerous.
“Ensuring underwater structural integrity is incredibly challenging,” explained Professor Li Zheng, a naval design expert at Shanghai Jiao Tong University, in a CCTV News interview. “At an 8-meter depth, significant pressure is exerted. Any flaw in design could lead to disaster.”
His family reportedly expressed worries about both the financial and physical risks during the early building stages. Undeterred, Zhang responded, “Only by attempting and achieving do you discover your true capabilities.”
Emblem of Grassroots Technological Innovation
Zhang’s accomplishment highlights a growing movement of innovative grassroots inventors in China's rural regions. While major government projects target technologies like hypersonic jets and AI-driven drones, individuals like Zhang develop solutions independently, exemplifying that hands-on, DIY innovation remains vibrant.
Recent figures from the China National Intellectual Property Administration (CNIPA) highlight an uptick in utility model patents from individuals residing in smaller provinces over the last five years. Many of these patents relate to farming, transportation, and energy efficiency. Although rarely making headlines, Zhang’s Big Black Fish has captured public imagination.
Looking ahead, Zhang plans to construct a larger submarine capable of longer underwater missions. This ambitious project will likely require additional resources and partnerships, but his decade-long journey suggests he has no plans to stop pioneering anytime soon.
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