Osamu Tezuka's Marine Express

To commemorate the 70th Anniversary of Osamu Tezuka's debut, Shigeto Ikehara, one of Tezuka's former assistants, adapted the anime film, Undersea Super Train: Marine Express, into a manga. Marine Express was aired as part of the 24 HOUR TV "LOVE SAVES THE EARTH" (24時間テレビ 「愛は地球を救う」, Niju Yojikan TV Ai Hachikyu wo Sukuu) program in 1979.

(from ebookjapan):

A wild, stormy night. In an old European-style mansion, Mr. Scheirlock, the chairman of the Construction Corporation of the Transoceanic Railroad, was assassinated and his body vanished. It is a few days before the imminent commissioning of the Marine Express, an undersea super-train...

The detective who discovered the corpse, Mr. Mustachio (A.K.A. Shunsaku Ban), boards the Marine Express with an unlicensed doctor, Black Jack, to pursue the truth of the case, but...?

The first volume begins with suspense over an undersea railroad!