Guests including South Korea's chief of naval operations posing in front of the new submarine Hong Beom Do at its launch ceremony on Tuesday at the Hyundai Heavy Industries dockyard in the south-eastern city of Ulsan.
The 1,800-tonne, diesel-electric vessel, armed with torpedoes and guided missiles, can travel at a maximum speed of 20 knots.
The submarine is named after a Korean independence activist who organised and conducted militant actions against Imperialist Japan from 1910 to 1945.