A video showing a submarine travelling across the surface of a water body is being widely shared on social media, where users have claimed that it shows Iran launching its "first domestically built nuclear submarine."An archived version of this claim can be seen here.(Archived versions of more posts sharing this claim can be seen here, here, and here.)Is it true?: No, the claim is false.The video dates back to 2023 and shows Japan's Taigei-class diesel-electric submarine, built by Mitsubishi, and not an Iranian nuclear submarine.Did Rahul Gandhi Make ‘Disgusting’ Remarks on Modi, Meloni? Claim Is MisleadingHow did we find out the truth?: We ran a reverse image search on the clip, which led us to an X post carrying the same video, shared on 26 June 2023.Its caption said, "Japan Maritime Self-Defense Force 4th Taigei-class Attack Submarine Raigei (SS-516)."Japan Maritime Self-Defense Force 4th Taigei-class Attack Submarine Raigei (SS-516) pic.twitter.com/nG8Dofj4dU— The Maritime (@themaritimenet) October 25, 2023We used the keywords 'Japan Raigei submarine 516' to look for more details about the naval vessel.This led us to a YouTube video shared on 17 October 2023 by a channel called 'Military Coverage', which had shared a longer version of the same video.The video identified the vessel as Japan's fourth Taigei-class submarine, Raigei JS-516 as well, making no mention of Iran.Another search using the same term, but in Japanese (潜水艦「雷鯨」516) led us to news reports about the vessel's launch.One such report, published on 17 October 2023 by Yahoo! Japan, said that the fourth Taigei-class submarine, Raigei, had been launched that day, and was the first to adopt a high-output diesel engine.This is a translated version of the report.The search also led us to the Japanese Ministry of Defence's website's page on its Taigei-class submarines.This page had shared two images of the Raigei diesel-electric submarine, with the same hull number of 516. (Swipe to view).The country's maritime wing had later issued a press release on 2 February 2025, mentioning that the submarine's handover ceremony would take place on 6 March 2025 in Japan's Kobe city.Iran's nuclear submarines: According to public data, Iran does not have any nuclear submarines, much less domestically built ones, as of August 2026. The only indigenously developed submarines it has belong to the Ghadir and Fateh classes, both of which are diesel-electric type submarines, the Australian Naval Institute notes.Conclusion: An old video of a Japanese submarine's launch is being shared to falsely claim that it shows Iran's first domestically built nuclear submarine.Viral Images of Nayanthara With Her Head Shaved at Tirumala Temple Are AI(Not convinced of a post or information you came across online and want it verified? Send us the details on WhatsApp at 9540511818 , or e-mail it to us at webqoof@thequint.com and we'll fact-check it for you. You can also read all our fact-checked stories here.)