The Joralemon Street Tunnel (/dʒəˈrælɛmən/, ju-RAL-e-mun), originally the Brooklyn–Battery Tunnel, is a pair of tubes carrying the IRT Lexington Avenue Line (4 and ​5 trains) of the New York City Subway under the East River between Bowling Green Park in Manhattan and Brooklyn Heights in Brooklyn, New York City.

The tubes descend 91 to 95 feet (28 to 29 m) below the mean high water level of the East River, with a maximum gradient of 3.1 percent.

During the tunnel's construction, a house at 58 Joralemon Street in Brooklyn was converted into a ventilation building and emergency exit.

[18][19] The steelwork for Contract 2 tunnels, including the Joralemon Street Tubes, was manufactured by the American Bridge Company.

[20] The tubes are lined with "rings" 22 inches (560 mm) wide, each of which is made of "plates" that form a perfect circle.

[6][13][14] The rings within the rocky sections, and within the segments of the tunnel above mean high water, generally weigh less than those placed within sandy ground or underneath the riverbed.

[8][13][16] Two construction shafts were built for the tunnel: one in Manhattan at South Ferry, and the other in Brooklyn at Henry and Joralemon Streets.

[28] Planning for the city's first subway line dates to the Rapid Transit Act, authorized by the New York State Legislature in 1894.

It called for a subway line from New York City Hall in lower Manhattan to the Upper West Side, where two branches would lead north into the Bronx.

However, the RTC expected that there would be competition for the route, which connected two large business districts and the city's two most populous boroughs.

The Board also knew that Belmont would submit a low bid to retain control of underground rapid transit for himself and his construction company.

[37] Contract 2, giving a lease of 35 years, was executed between the commission and the Rapid Transit Construction Company on September 11, 1902.

After the headings had been driven approximately 100 feet (30 m), two thick brick walls were constructed at each end, creating air locks.

[13][17] After the shields were driven, temporary wooden beams were placed to reinforce the excavations until the cast-iron tubes were assembled.

[43] In June 1904, the RTC said the city was not responsible for repairs to the houses, although contractors were digging another shaft to relieve air pressure in the excavation.

In March 1905, one of the tubes suddenly lost pressure in a "blowout", propelling a worker through the mud and into the air, although he survived.

[52] During this time, Parsons and his successor George S. Rice discovered that the ceilings of the tubes had flattened downward; trains could still run through the tunnels, but the roofs would be scraped at high speeds.

[60] By that July, the city's Public Service Commission ordered that additional shifts of workers be hired for the Joralemon project so that test trains could start running through the tunnels within three months.

[61] The first test train, carrying officials, reporters, and construction engineers, ran through the Joralemon Street Tunnel to Brooklyn at 12:40 p.m. on November 27, 1907.

[65] In Brooklyn, service proceeded beneath Joralemon, Fulton, and Willoughby Streets, originally terminating at Atlantic Avenue.

A Brooklyn-bound train derailed during the morning rush hour of January 1, 1965, blocking service for half a day, although no one was harmed.

[73] During the evening rush hour of March 17, 1984, another train derailed with 1,500 passengers while traveling over a track that was being repaired, but again, no one was killed or seriously injured.

[76] It was one of seven East River subway tunnels flooded on October 29, 2012, as Hurricane Sandy's storm surge inundated Lower Manhattan.