The heart of the Hudson and Manhattan Railroad Co.  / Hudson Tubes consisted [and still consists] of a series of double tube tunnels, each tube with a diameter of just over 15 feet; this trait gave the  entire system the nickname, Hudson Tubes or The Tubes and. later, Hudson Rapid Tubes.

When the first attempt was made [on what later became the uptown tunnels], there was no excavation shield and no iron construction because the Chief Engineer,  Haskins,  believed that the river silt was strong enough with the help of compressed air support to hold in place until a brick lining, 2½ feet thick, was in place to support the tunnels’ structure without distortion. 

His plan was to excavate the tunnel, filling it with 35 pounds of air pressure to expel water and hold the tunnel's iron-plate liners, thin steel plates 3/16th inch thick; then sheathe that in a brick lining. He was able to build out about 1,200 feet from Jersey City until the July 21, 1880  blowout with 20 deaths and then a second blowout ended the project.

When construction of now two tunnels was resumed by a new company,  tubular cast iron construction was employed. Thus there are three basic kinds of tunneling: the earliest subaqueous tunnel, i.e.. the northernmost uptown tunnel used brick lining; the southern uptown tunnel and the downtown subaqueous tunnels employed the tubular cast iron construction, while the later subterranean stations in Manhattan employed cut and cover construction and concrete tunnels. [Both these images are from the Terry Kennedy Collection.]

There were two river crossings tying together a series of stations in New Jersey (with one exception, all in Hudson County) with a series of stations in Manhattan. The southern set of trans-river tunnels [ "Montgomery-Cortlandt Tunnels"] connected Cortlandt Street (at Church Street) in Manhattan's financial district with Montgomery Street in lower Jersey City where the Pennsylvania Railroad's main New York station was located. 

The expandable image above is an idealized view from an H&M stock certificate, showing the downtown connection between the Pennsylvania RR Station in Jersey City on the left and the new Hudson Terminal [later replaced by the World Trade Center] in Manhattan on the right with the Tubes running under the river. The expandable sketch is from 2002 [from the Tubes Restoration site] but shows the tunnel-pair as it had been built 100 years previously.

The two major - and massive - station constructions were at Hudson Terminal [the later World Trade Center] and Exchange Place, Jersey City.

Contemporary accounts report Exchange Place station as being  blasted out of solid rock 85 feet below street level. The station was almost 1,000 feet long, 150' wide and was apparently directly under the PRR station. Its walls and roof were finished with concrete. 

The station was originally designed for 4 if not 5 tracks, two of which were to be for through trains to Manhattan, two for local trains terminating at the PRR Station. Initial plans called for  Exchange Place being  the H&M's branch off point to the Central Railroad of New Jersey terminal on Johnson Ave [Click the image to see the planned route full size.].

It was assumed that the majority of passenger traffic would be entering the H&M station from the PRR station, not from the street. Consequently of the six elevator entrances at the station  two lead from the PRR station to the street, while four elevators were to run between the PRR's platforms and the H&M Exchange Place platforms. [Two of the four elevators to the H&M platforms were replaced by escalators in the PATH period.]

Above the Tubes' massive Cortlandt Street station rose Hudson Terminal. At the time of its construction the 22 story twin towers of the "Hudson Terminal Buildings" made up the largest office complex in the world.Expand image and then click 2. Construction History to return [Also see 5. Tube Stations for more details on the construction of Hudson Terminal.]

Beneath Sixth Avenue in Manhattan a pair of parallel tunnels ran south from 33rd Street 1.2 miles to Christopher Street. At that point the line curved sharply to the southwest, running under Christopher Street to the river. Then, after a double jog, the route crossed the river, which here is close to a mile wide, through the 5,600 foot tunnels originally begun in 1874. 

Just under the New Jersey shore,  approximately at the Jersey City Hoboken boundary line, there was a complicated junction inside a planned double deck caisson [which ultimately evolved into a single level junction] that was sunk 86 feet below high water and the tubes split. A short northbound extension went through a series of very sharp curves ending in Hoboken underneath the former DL&W Railroad Terminal.  Expand image to the left for a good view of this complicated junction as presented in a contemporary issue of Scribner's Magazine  and then click 2. Construction History to return

Two other tunnels left this northern junction and headed southward, parallel to the river until just before Grove Street Station when they combined in a similar junction, although not  in a caisson, with the Hudson Terminal /  Journal Square segments of the Tubes, with  two tunnels coming from Lower Manhattan. The combined tubes headed westwards through Jersey City coming to the surface just before Journal Square.  For an interesting schematic of the entire subterranean Tube layout - from the New York City Subway Resources website -

The combined tunnel route came to the surface cutting through the ridge of the Palisades in Jersey City at Journal Square (originally called Summit Avenue) and continued westward through the marshy Meadows through Manhattan Transfer in Harrison to Newark. The section of the Tubes west of Journal Square, was a joint operation of the Pennsylvania RR and the H&M operated under the legal name "Joint Service Electric Railroad" and requiring a separate or surcharge fare. 

As the Tubes came above ground, just before Journal Square,  they were joined on the north by the mainline of the Pennsylvania Railroad. These PRR trains had  run westwards on a viaduct over Railroad Avenue [which was re-named Christopher Columbus Drive when the viaduct was demolished about 25 years ago] from Grove and Henderson Streets [the tracks had reached Grove Street on an embankment from the PRR terminal at the river.

To power the new railroad the H&M constructed its own powerhouse in Lower Jersey City between the Exchange Place and Erie stations, near the intersection of  Washington Street and Second Street.  John Oakman designed a neo-Norman structure that became an immediate landmark in the area, and not merely because of its height and  bulk. The Power House was closed in 1929 when it became more economical to purchase electricity from outside sources. [Currently the Jersey City Landmarks Conservancy is conducting a campaign to restore the Powerhouse structure and turn it into a productive resource. Contemporary photo from David Pirmann]