Early history

The oldest line to become part of the B Division was the BMT Lexington Avenue Line, opened in 1885. A large system of elevated railways in Brooklyn was formed by 1908 by the Brooklyn Rapid Transit Company (BRT), crossing the Brooklyn Bridge and Williamsburg Bridge to Manhattan terminals. With the Dual Contracts, signed in 1913, the BRT acquired extensions outward into Queens, as well as through Lower and Midtown Manhattan. The BRT became the Brooklyn–Manhattan Transit Corporation in 1923 after a bankruptcy.

The Independent Subway System (IND) was created by the city in the 1920s and 1930s as a third system, operated by the city, competing with the BMT and Interborough Rapid Transit Company (IRT). The city took over operations of the BMT and IRT in 1940, consolidating ownership of the three systems into one. Since the original IRT tunnels were smaller, it has remained a separate division to this day.

IND before 1967

IND services were labeled on maps and signs starting with the opening of the first line in 1932. Six letters—A to F—were assigned to the major services, sorted by the north terminal and midtown line, and express services had single letters, while local services had double letters. G and H were assigned to lesser services, which did not enter Manhattan. The following labels were used from 1940 to 1967:

Consolidation of operations

Until 1954 and 1955, when the Culver Ramp and 60th Street Tunnel Connection opened, the BMT and IND trackage was not connected. The early joint services using these connections operated similarly to trackage rights; it was not until the Chrystie Street Connection opened in 1967 that the ex-BMT and IND systems were consolidated operationally.

Beginning in 1924, BMT services were designated by number.^[4] The city assigned letters (J and up)—generally following the IND pattern of double letters for local services—in the early 1960s to prepare for the 1967 Chrystie Street Connection. Only Southern Division routes (1–4 or N–T) were labeled on maps, but all services except remnants of the old els were assigned letters:^[5][6]

* Unofficially signed as "M", or sometimes "S".

In 1967, the Culver and Franklin Shuttles became SS—the standard shuttle designation—and the Myrtle Local ("Myrtle (Jay)"),^[7] discontinued in 1969) was labeled MJ.

After 1967

The 1967 opening of the Chrystie Street Connection resulted in a number of changes. The following services have been operated since then:

• A Eighth Avenue Express, 1967–present
• B Sixth Avenue Express, 1967–present
• C Eighth Avenue Local, 1967–present (CC until 1985)
• D Sixth Avenue Express, 1967–present
• E Eighth Avenue Local, 1967–present
• EE Broadway Local, 1967–1976
• F Sixth Avenue Local, 1967–present
• G Brooklyn-Queens Crosstown Local, 1967–present (GG until 1985)
• J Nassau Street Express, 1967–present (QJ until 1973)
• K Broadway Brooklyn Local, 1967–1976 (JJ from 1967 to 1968; KK from 1968 to 1973)
• K Eighth Avenue Local, 1967 – 1988 (AA until 1985)
• L 14th Street-Canarsie Local, 1967–present (LL until 1985)
• M Nassau Street Local, 1967–2010; Sixth Ave Local, 2010–present
• MJ Myrtle Avenue Local, 1967–1969
• N Broadway Express, 1967–present
• NX Broadway Express, 1967–1968
• Q Broadway Express, 1967–present (QB until 1985)
• R Broadway Local, 1967–present (RR until 1985)
• RJ Nassau Street Local, 1967–1968
• S Franklin Avenue Shuttle, 1967–present (SS until 1985)
• S Rockaway Park Shuttle, 1967–1972, 1985–present (HH from 1967 to 1972 and H from 1985 to 1992 and 2012–2013; part of the A and CC in between)
• SS Culver Shuttle, 1967–1975
• TT West End Shuttle, 1967–1968
• V Sixth Avenue Local, 2001–2010
• W Broadway Local, 2001–2010, 2016–present
• Z Nassau Street Express, 1988–present