The Brooklyn Manhattan Transit company, or 'the BMT,' was one of the two privately owned transit
companies whose subway
operations were consolidated, along with the city owned Independent Subway
into the current New York City subway
The BMT was itself an agglomeration of many transit routes often built by other companies which were bought out. The first lines which were to become part of the BMT were railways built in the middle of the 19th century through the then farmland of Southern Brooklyn to the resort at Coney Island. The Brighton Line (part of today's D and Q Trains), the Culver line (pert of today's F Train), the Sea Beach line (part of today's N Train) and the West End Line (part of today's B Train) all got their start in this way.
Later on in the 19th century, the developed part of the city of Brooklyn began to build elevated commuter railways under the auspices of the Brooklyn Rapid Transit corporation (BRT), the ancestor of the BMT. This network of elevated railways was quite extensive by the dawn of the 20th century. In general the elevateds converged on downtown Brooklyn and ended at the Fulton Ferry. Later, after it was completed in 1886, they traversed tracks on the Brooklyn Bridge to Park Row in Manhattan. Others fed to the Williamsburg Bridge after it was completed in 1903. Among the major elevateds were the Fulton Avenue Elevated (the surviving piece of which is used by today's A Train), the Broadway Elevated (today's J and Z Trains), and the Myrtle Avenue Elevated (today's M Train), as well as many which no longer exist including the Lafayette Avenue elevated and the Fifth Avenue Elevated through Park Slope. The former resort railways of Southern Brooklyn were gradually tied into this elevated network. In 1898, Brooklyn joined with Manhattan to form the greater New York City that we know today.
The other major transit holder at the turn of the century in New York was the Interboro Rapid Transit corporation (IRT). The IRT had elevated lines in Manhattan and the Bronx, and the first piece of the New York City Subway was completed in Manhattan by the Interboro Rapid Transit in 1904. It was shortly thereafter extended through a tunnel under the East River to Brooklyn, bringing the IRT into direct competition with the BRT. The BRT secured a contract with the city to build its own subway between Manhattan and Brooklyn. This route ran up Fourth Avenue, through a tunnel under the East River to the battery, and then up Broadway in Manhattan. This line is today's N and R Trains through Brooklyn and Manhattan. Many of the lines in Southern Brooklyn were now connected into this subway in addition to the Fifth Avenue elevated. Another line was constructed using old Long Island Railway tracks in Canarsie and through Northern Brookyn and under the river to 14th street in Manhattan (today's L Train).
The next period of subway expansion, in the late teens and early 20s, was the Dual Contracts era, in which the city contracted out to the BRT and IRT the work of expanding the system in routes which it determined. The BRT connected the Brighton line via a subway under Flatbush Avenue to the tracks over the Manhattan Bridge. The two companies jointly built and operated the Astoria and Flushing lines in Queens (today's 7 Train and the Queens part of the N Train. The BRT was now in three boroughs. In 1919 the BRT was responsible for New York City's Worst Subway Disaster, the Malbone Street wreck, in which a scab motor man filling in for strikers crashed a.train along the route that is today's Franklin Avenue Shuttle. Around this time the BRT was facing financial problems and reorganized as the Brooklyn Manhattan Transit, or BMT.
In the late 20s and early 30s, the city, under mayor John Hyland, a disgruntled former employee of the BRT, embarked on a project to build and operate its own subway lines, competing directly with the BMT and IRT in the hopes of driving them to bankruptcy and allowing the city to assume control of all transit operations. The Independent, or IND, as the city owned lines were called, took business from the BMT by building a subway under Fulton Avenue and Lafayette Avenue where there were already BMT elevateds, as well as building lines elsewhere in all the boroughs. As the IRT and BMT were built to different width and tunnel clearance specifications, the city chose to build the IND to BMT standards to facilitate the eventual integration of those two systems.
Finally, in 1940, the BMT and IRT were willing to sell and the city assumed all transit operations. The new city transit agency went about consolidating the various lines, and making both track and transfer connections between the formerly separate systems. The IND crosstown line was connected to the BMT Culver line, the BMT tunnels were connected to the Queens Boulevard line, and stations of all three systems were connected by passageways. The city tore down some of the former BMT elevateds, including the Fifth Avenue elevated and the now redundant Fulton Avenue and Lafayette Avenue ones, although part of the Fulton Avenue elevated line was incorporated into the A train. The three system (BMT, IRT, and IND) distinction remained on maps though, until 1967, when the Chrystie Street connection from the Manhattan Bridge to the Sixth avenue line was completed and the lines of the IND and BMT were sufficiently intermixed to make division irrelevant. Currently the Metropolitan Transportation Authority operates all of the lines of the New York City subway.