Compressed Air in the Tunnels

Work never stopped on the Pennsylvania Railroad’s tunneling projects; there were three 8-hour shifts a day, 7 days a week. As the workers dug under the river bed, compressed air was pumped in to keep the water out of the tunnels. To bore under the river, the engineers used a Greathead shield, a steel cylinder with a diameter of 23 feet that weighed nearly 200 tons.