The longest undersea tunnel in the world. Eurotunnel crossing the Strait of Dover

The Eurotunnel, a 38km long undersea tunnel that passes under the Strait of Dover, was completed in 1991.

Kawasaki Heavy Industries, Ltd. completed the tunnel excavation from the more difficult French side using giant high-tech tunnel boring machines, and took only 3 years to complete the project.
In the case of large scale tunnels, Japanese machines are set there, automatically digging and cementing the walls.  All over the world, such work is left to Japanese tunnel boring machines.