Japan–Korea Undersea Tunnel

The Japan–Korea Undersea Tunnel, or Korea–Japan Undersea Tunnel, is a proposed tunnel project to connect Japan with South Korea via an undersea tunnel crossing the Korea Strait that would use the strait islands of Iki and Tsushima, a straight-line distance of approximately 128 kilometers (80 mi) at its shortest.

The proposal, which has been under discussion intermittently since 1917, was followed with more concrete planning during the early 1940s. It was not pursued, however, until after World War II.

In early 2008, the proposal came under renewed discussions by 10 senior Japanese lawmakers, who established a new committee to pursue it. That was followed by a study group from both countries in early 2009 that agreed to form a committee for the creation of specific construction plans. Its head, Huh Moon-do, a former director of South Korea's National Unification Board and a key member of the former Chun Doo-hwan government, said that the tunnel would help regional economics and would "play a key role in pursuing bilateral free trade talks," which are currently stalled.

The proposed tunnel would be more than 200 km (120 mi) long and serve a portion of freight traffic, as well as some of the approximately 20,000 people who travel daily between the countries.

However, since the Great East Japan earthquake and tsunami in March 2011, the COVID-19 pandemic in 2020 and 2022, and with the assassination of former Japanese Prime Minister Shinzo Abe in July 2022, one of the biggest proponents of the tunnel, the Unification Church, faced huge criticisms in Japan for collecting donations from Japanese believers with manipulative and coercive tactics. Consequentially public anger against the tunnel grew in Japan.