[1] One of three subway networks that became part of the modern New York City Subway, the IND was intended to be fully owned and operated by the municipal government, in contrast to the privately operated or jointly funded Interborough Rapid Transit Company (IRT) and Brooklyn–Manhattan Transit Corporation (BMT) companies.

For operational purposes, the IND and BMT lines and services are referred to jointly as the B Division.

The original IND system was entirely underground in the four boroughs that it served, with the exception of a short section of the IND Culver Line containing two stations spanning the Gowanus Canal in the Gowanus section of Brooklyn.

[4][5] The New York City Transit Commission was formed in 1921 to develop a plan to reduce overcrowding on the subways.

[1] On July 8, 1931, the first train of R1s left Coney Island at 11:35am and ran via the BMT Sea Beach Line to Times Square.

[1] The new IND Eighth Avenue Line was built using 1,000,000 cubic yards (27,000,000 cu ft) of concrete and 150,000 short tons (140,000,000 kg) of steel.

[1] At the time of the line's opening, other portions of the Independent Subway System were under construction, including five underwater tunnels:[1] There was some vandalism on the IND Eighth Avenue Line's opening day, as some of the uptown stations were broken into by people who clogged turnstile slots with gum and other objects.

[10] E trains ran local to Hudson Terminal (today's World Trade Center) in Manhattan, while the GG (predecessor to current G service) ran as a shuttle service between Queens Plaza and Nassau Avenue on the IND Crosstown Line, which opened on the same day.

[1] The first short section of the IND Culver Line opened on March 20, 1933, taking Eighth Avenue Express A trains (and for about a month from July to August C trains) south from Jay Street to Bergen Street.

E trains, which ran from Jackson Heights, Queens to Hudson Terminal, were shifted to the new line to East Broadway.

[23] Two express tracks were built on the portion under Houston Street until Essex Street-Avenue A; the tracks were intended to travel under the East River and connect with the never-built IND Worth Street Line in Williamsburg, Brooklyn.

As the city wanted to tear down the IRT Sixth Avenue Line right away and save on the costs of shoring it up while construction proceeded underneath it, the IRT Sixth Avenue Line was purchased for $12.5 million and terminated by the city on December 5, 1938.

[28][31] On December 31, 1936, the Queens Boulevard Line was extended from Roosevelt Avenue to Kew Gardens–Union Turnpike.

[11][33][35][36] That day, express service began on the Queens Boulevard Line during rush hours, with E trains running express west of 71st–Continental Avenues, and GG trains taking over the local during rush hours.

The World's Fair line ran via a connection through the Jamaica Yard and through Flushing Meadows–Corona Park along the current right-of-way of the Van Wyck Expressway.

[12] Mayor John Hylan proposed some never-built lines in 1922 even before the first leg of the IND was completed.

[42] It would have added over 100 miles of new routes in Manhattan, Brooklyn, Queens, and the Bronx, merging with, intersecting or extending the existing IND rights-of way.

It was claimed that this expansion, combined with the operating IRT, BMT, and IND lines, would provide subway service within a half mile of anyone's doorstep within these four boroughs.

Therefore, the line was going to be extended to 184th Place with a station at 179th Street with two island platforms, sufficient entrances and exits, and storage for four ten-car trains.

[57] This extension was delayed due to the Great Depression and World War II.

IND trains begin operating over the BMT Culver Line to Coney Island–Stillwell Avenue.

The construction project extended the lower level LIRR tunnel and involved a number of other elements, including the integration of ventilation plants, lowering a sewer siphon 50 feet, rehabilitation of elements of the existing line, mitigating ground water, diverting trains which continued to run through the project area and widening of the entry point to the Queens Boulevard Line to six tracks.

As originally designed, the IND train identification scheme was based on three things: the Manhattan trunk line served (8th Avenue or 6th Avenue), the northern branch line served (Washington Heights, Grand Concourse/Bronx, or Queens Boulevard), and the service level (Express or Local).

[80] The first designations were as follows: Virtually all possibilities were used at one time or another, either in regular service or as brief special routes.

[80] After the Chrystie Street Connection opened, the original IND Service Letter scheme was gradually abandoned.

Initial plans called for stations to be built with 660 feet (201 m) long platforms to accommodate trains of eleven 60-foot (18.3 m) cars.

There were two exceptions: 96th Street was 615 feet (187 m) on both levels, as that was the standard length of platforms built for the IND after the 1940s.

In 34th Street–Herald Square, the uptown platform was originally 745 feet (227 m), long enough to hold a 12-car train of 60-foot (18.3 m) cars.

[1] In the IND Second System, planned stations would have been 700 to 720 feet (213 to 219 m) long and tile work would have been more "modern".