The PATH Christopher Street Station is part of the original H&M line that opened in 1908, running between Hoboken and 19th Street in Manhattan.

The Hudson and Manhattan Railroad Tunnel, now part of the interstate rapid transit system known as the Port Authority Trans-Hudson (PATH), is one of New York City's earliest subway systems. Construction of the subway tunnel under the Hudson River between New York and New Jersey stretched out over a period of more than three decades beginning in 1874, predating the first New York City subway (although the IRT subway opened beforehand, initial construction of the first New York City subway did not begin until 1900). The Hudson & Manhattan Tunnel served as a proving ground for new underwater tunneling methods and as a training school for engineers who later became leaders in shield-driven tunnel construction.

The history of the PATH system traces back to the incorporation of the Hudson Tunnel Railroad Company on May 26, 1873, led by president Colonel De Witt Clinton Haskin, a businessman from Upstate New York who made his fortune on the construction of the California Pacific Railroad and in Utah silver mines. Haskin conceived the idea to construct a tunnel under the Hudson River while spending part of a night on a ferryboat stuck in the ice between Jersey City and Manhattan. Construction of the tunnel began on November 17, 1874 with the sinking of a shaft on Fifteenth Street in Jersey City. However, work was halted for a five-year period on December 15, 1874 due to litigation by Delaware, Lackwanna & Western Railroad for the amount of monetary compensation for property acquired through eminent domain. Construction of the first tunnel under the Hudson River did not resume until the injunction was dissolved on September 22, 1879.

The PATH 9th Street Station is located below Sixth Avenue in Manhattan's Greenwich Village.

Using only manual labor with shovels and picks, excavation of the tunnel proceeded very slowly, advancing an average of just four to five feet (1.2-1.5 m) per day. The ceiling of the tunnel was lined with ¼-inch (6.3 mm) thick iron plates and the tunnel was encircled with a 2 ½ feet (76 cm) thick layer of bricks. A tunneling shield was not used in the excavation process because it was believed that the silt was strong enough to hold back the compressed air in the tunnel. A major blowout occurred on July 21, 1880 when a leak developed on top of the tunnel, letting out compressed air into the 30 feet (9.1 m) of silt between the tunnel and the river bottom. The hole grew larger and river water began to flood the tunnel, trapping 28 men inside. Eight men miraculously escaped through the air lock, but the remaining workers were trapped and killed.

The flooded tunnel could not be pumped out afterward so a caisson was sunk to create a large work chamber and repair the completed sections of the tunnel. Construction resumed and a new caisson was sunk at the foot of Morton Street to begin excavation from the New York side. General William Sooy Smith joined the project as chief engineer and introduced a number of improvements. A bulkhead was added near the tunnel heading that included airlocks and could be quickly accessed by workers in the event of a blowout. Additionally, the tunnel walls were lined with concrete instead of brick and a pressurized discharge pipe was added to transport excavated silt out of the tunnel.

A hundred ASCE members from across North America received a special tour of the construction project from General Smith on January 19, 1882, passing through the airlock to inspect portions of the tunnel. Later that day, the same group of engineers visited the Brooklyn Bridge, which was also under construction. Although construction had steadily progressed for two years since the major blowout, work was suspended on November 4, 1882 after the death of Haskin's associate and financial backer Trevor W. Park. At that time, the north tunnel extended 1,542 feet (470 m) from the New Jersey side and 75 feet (23 m) from the New York side, while the south tunnel extended 562 feet (171 m) from the New Jersey side.

A plaque designating the H&M Tubes as a National Historic Civil Engineering Landmark was unveiled at the World Trade Center PATH Station in 1978.

Construction resumed in 1889 with financial backing by English investors, but this time using the shield method of tunneling that had proven successful in the construction of the Beach Pneumatic Subway in New York City and the London Subway. The tunneling shield was an iron cylinder that was hydraulically jacked forward with 1,327 tons (1,204 t) of pressure. It was divided into compartments and had a number of doors that temporarily supported the newly excavated portions of the tunnel before the permanent cast iron plates were bolted together to form the cylindrical tunnel walls. However, work again came to a halt in 1892 because of financial difficulties. By this time, the north tube had been extended to 3,916 feet (1,194 m) from the New Jersey shaft and 160 feet (49 m) from the New York shaft. Meanwhile, the south tunnel had been extended 570 feet (174 m) from its New Jersey shaft.

On February 11, 1902 a new company, the New York and New Jersey Railroad, was formed to undertake the completion of the project. Assured of adequate financing, the work was resumed under the direction of President William G. McAdoo, a young lawyer from Tennessee who would later serve as the Secretary of the Treasury under President Woodrow Wilson and as a United States Senator from California. Charles M. Jacobs was the chief engineer of the project and was assisted by deputy chief engineer J. Vipond Davies (an early president of the ASCE Met Section). The New York and New Jersey Railroad Company was later consolidated into the Hudson and Manhattan Railroad (H&M) on December 1, 1906.

In spite of all of the numerous obstacles, the uptown tunnels were finally brought to a successful completion. The north tunnel was holed through on March 11, 1904 and the south tunnel was holed through on September 29, 1905. During the construction of the south tunnel, improvements in the tunneling shield allowed the tunnel to advance at a rate of up to 72 feet (22 m) per day. Both tunnels were 5,650 feet (1,722 m) long at a maximum depth of 97 feet (30 m) below the river. The diameter of each tube was 15 feet and 3 inches (4.6 m). The cut-and-cover method of construction was used for the tunnel segments in Manhattan.

The 23rd Street Station opened on June 15, 1908 when the line was extended north from 19th Street.

On the afternoon of February 25, 1908, President Theodore Roosevelt pressed a button from the White House that turned on electrical power to the system. The first train filled with dignitaries including New York Governor Charles Hughes, New Jersey Governor John Fort, August Belmont, Cornelius Vanderbilt, and George Westinghouse passed through the "McAdoo Tunnel" from Sixth Avenue and 19th Street in Manhattan to the Lackawanna Terminal in Hoboken in just 10 ½ minutes. The H&M Railroad began its operation at midnight and nearly 100,000 passengers used the system during the first day of service.

Meanwhile, a second set of tunnels was constructed between Jersey City and the Hudson Terminal in Lower Manhattan (now the site of the World Trade Center) beginning in September 1905. These tunnels were 5,976 feet (1,821 m) long at a maximum depth of 92 feet (28 m) below the river. Service on the downtown H&M tunnels between began on July 19, 1909, while the uptown tunnels were extended north to a new terminal station at Sixth Avenue and 33rd Street (Greeley Square) on November 10, 1910. Each of the terminal stations was designed with platforms on both sides of the track so that passengers could exit one side of the train while passengers could enter on the other side. The McAdoo System was extended to Newark on November 26, 1911.

In its early years the Hudson & Manhattan Railroad was well patronized and profitable but ridership began to drop off drastically after the opening of the Holland and Lincoln Tunnels (due to the popularity of the automobile) and during the depression of the 1930s. In the 1950s the Hudson and Manhattan Railroad Company was in bankruptcy and the condition of the railroad had deteriorated seriously from lack of maintenance. To avoid total abandonment the Port Authority of New York & New Jersey agreed took over the railroad in 1962 and shifted the location of its proposed World Trade Center in Lower Manhattan from the South Street Seaport area (adjacent to the East River) to the site of H&M's Hudson Terminal between Greenwich and Church Streets, building a new underground station that opened in 1971. Following the takeover of the H&M Railroad, the Port Authority made extensive repairs and improvements, including new rolling stock, and began operating the PATH system as we know today.

In April 1978 the Society's Board of Direction voted to designate the Hudson and Manhattan Railroad Tunnel a National Historic Civil Engineering Landmark. The nomination for the designation was submitted by the ASCE Met Section in 1977 after a unanimous vote of the Section's board. The unveiling of two bronze plaques designating the Hudson and Manhattan Railroad Tunnel as a Historic Civil Engineering Landmark occurred on October 31, 1978. One plaque was placed in the Hoboken Terminal and another plaque was placed in the World Trade Center.

A plaque designating the H&M Tunnels as a National Historic Civil Engineering Landmark was also unveiled at the Hoboken Terminal in New Jersey.

Both ceremonies were well attended and addressed by Chairman Alan Sagner of the Port Authority and Peter Goldmark, the Port Authority's executive director. Officials representing the governors of both states and the mayors of New York City and Hoboken addressed the audience. ASCE President Walter E. Blessey unveiled the plaques and presented them to the Port Authority in a formal address in which he described the Society's national historic civil engineering landmarks program. Members of the family of William G. McAdoo attended the ceremony and his grandson, Brice McAdoo Clagett, spoke about how his grandfather headed the organization that finally completed the railroad project in 1910 after many years of starts and abandonments beginning in 1874.

At the close of the ceremony in the Hoboken Terminal those attending boarded a special train for a trip through the tunnel to New York. Approaching the World Trade Center, the train was halted in the tunnel and the passengers transferred to flat cars attached to the train for an inspection of the tunnel and a description of the structure by John F. Hoban, the Port Authority's director of rail transportation. The train then continued to the World Trade Center for the ceremony unveiling the plaque in New York.