THE tunnel diggers gazed in disbelief at what they had uncovered. The year was 1912. Deep beneath the streets of New York City, while excavating an extension of the newly built subway, they had broken into a large hidden chamber. The room was magnificently furnished—like a palace! Along its length were mirrors, chandeliers, and frescoes. Wood paneling, crumbling with age, still adorned the walls. In the middle of the room stood a decorative fountain, its bubbling long silent.The room led to a tunnel. To the workers’ astonishment, there sat a graciously decorated 22-passenger subway car on its rails. Had there been another subway under New York before the one they were digging? Who could have built this place?Underground passages have been in use for mining, supplying water, and military exploits for thousands of years. Mechanized underground transport of passengers, however, came about much more recently. In the early 1800s, thoroughfares in London, England, were choked with every imaginable type of contemporary vehicle, not to mention pedestrian traffic. Thousands crossed the Thames daily, either by ferry or over London Bridge. At times, progress was so slow that merchants could only watch helplessly as the products they were trying to get to market withered in the sun. Marc Isambard Brunel, a French engineer living in England, had an idea that would eventually help to alleviate some of London’s transportation troubles. Brunel had once observed a shipworm working its way through a piece of hard oak. He noted that only the head of the little mollusk was protected by a shell. The shipworm used the serrated edges of its shell to bore through the wood. As it progressed, it left behind in its burrow a smooth protective coating of lime. Applying this principle, Brunel patented a large cast-iron tunneling shield, to be pushed forward through the ground by jacks. As workers removed the earth from inside the shield, the shield would prevent collapse.Marc Isambard Brunel, a French engineer living in England, had an idea that would eventually help to alleviate some of London’s transportation troubles. Brunel had once observed a shipworm working its way through a piece of hard oak. He noted that only the head of the little mollusk was protected by a shell.