EXPLAINER Why Unification Church is so desperate for Korea-Japan undersea tunnel

Unification Church leader Han Hak-ja, second from left, inspects the exploratory drilling site for the Korea-Japan undersea tunnel project in Karatsu, Saga Prefecture, Japan, during the 30th anniversary ceremony for the drilling in Nov. 14, 2016. Courtesy of Family Federation for World Peace and Unification

The Unification Church's long-cherished Korea-Japan undersea tunnel proposal is regaining public attention after Rep. Chun Jae-soo of the ruling Democratic Party of Korea resigned as oceans minister last week. He stepped down amid allegations that the church bribed him and other politicians to win support for the project.

Questions are mounting over why the church has spent more than four decades lobbying for a megaproject that the government has already concluded makes little economic sense.

The tunnel plan dates back to 1981, when the church's founder, Moon Sun-myung, proposed the construction of a "Great Asian Highway" to link major Asian cities by road.

"This would be a great international highway around which freedom is guaranteed," Moon said that year at the 10th International Conference on the Unity of the Sciences in Seoul.

His proposal echoed the Japanese Empire’s idea from the 1910s and 1940s to connect the island nation to the continent by land to improve wartime logistics. Former Korean presidents — including Roh Tae-woo, Kim Dae-jung and Roh Moo-hyun — also brought up the tunnel project during meetings with their Japanese counterparts.

Calling Korea the "Adam nation" and Japan the "Eve nation," Moon strongly emphasized the Korea-Japan undersea tunnel as the starting point of a providential effort to unite the world physically and spiritually. The project became central to the church's theology and identity.

The church has proposed a tunnel running from Japan's Kyushu and Tsushima islands to Korea's Geoje Island and onward to Busan, with some proposed routes stretching nearly 250 kilometers under the Korea Strait. If built, it would be the world's longest undersea tunnel.

In the 1980s, church-affiliated entities began exploratory drilling in Japan and later bought land in Kyushu, leading some believers to think that the project was already underway.

However, the Korean land ministry ruled the project economically unsound.

In 2011, the ministry commissioned the Korea Transport Institute to study the feasibility of Korea-Japan and Korea-China undersea tunnels.

The analysis estimated that the Korea-Japan tunnel would cost more than 100 trillion won ($86.2 billion at the time) and concluded that its benefit-cost ratio fell far below the 0.8 threshold commonly used to justify major infrastructure projects, effectively declaring the tunnel idea as economically unjustifiable.

"We expect the negative findings to calm political debate," a ministry official said at the time. The church, however, continued to pursue the project.

Participants pose at the Plaza Hotel Seoul, March 31, 2021, during a symposium co-hosted by the World Peace Tunnel Foundation and the Korea Undersea Tunnel Research Association to discuss the global trend of undersea tunnel construction and the Korea-Japan undersea tunnel. Courtesy of Korea Undersea Tunnel Research Association

Treating the tunnel as a religious mission, the church continued efforts to secure support from politicians in Busan, including the DPK's Chun, a lawmaker who represents one of the city's districts.

Warning about the possibility of too much economic dependence on Japan, however, Chun and most of his fellow liberal party lawmakers have remained skeptical about the plan.

Conservative politicians have taken the opposite stance.

Ahead of the Busan mayoral by-election in 2021, then-People Power Party interim leader Kim Chong-in publicly said the party would consider the tunnel's construction, and some business leaders such as former Kumho Asiana Group Chairman Park Sam-koo also backed the idea.

To broaden support for the idea, the church set up secular-sounding bodies such as the World Peace Tunnel Foundation in Korea and the International Highway Foundation in Japan.

These groups have organized seminars, site visits and publicity campaigns that frame the tunnel as a neutral peace and development initiative. High-profile advocates including U.S. investor Jim Rogers have also been enlisted to argue that the tunnel could transform regional logistics and tourism once security tensions ease.

Since the 2022 assassination of former Japanese Prime Minister Shinzo Abe led to media investigations into the church's ties with Japanese politicians, however, momentum for the tunnel project has slowed sharply in Japan.

Given the recent scandal involving the church and Korean politicians, it is also expected to be unlikely for the project to be revisited in Korea.