The M2, M4 and M6 were three similar series of electric multiple unit rail cars produced by the Budd Company (M2), Tokyu Car Corporation (M4), and Morrison-Knudsen (M6) for the Metropolitan Transportation Authority (MTA) and the Connecticut Department of Transportation (ConnDOT). Initially branded as the Cosmopolitans, the cars were later more popularly known under their model names, M2 (1970s cars), M4 (1980s cars), M6 (1990s cars). They ran on the New Haven Line (then part of Penn Central, now a part of Metro-North) for most of their service life. The M4s and M6s were retired by Metro-North in 2015, followed by the last M2s in 2018. They have been largely replaced by new M8 railcars. One pair of M2s has been preserved at the Danbury Railway Museum in Connecticut. Overview The M2 cars were built primarily by General Electric in a consortium with the Budd Company, Canadian Vickers and Avco between 1972 and 1977. They were initially branded as Cosmopolitans; both the model and brand name followed the pattern set up by the M1/M1A series (the Metropolitans) in use on the Long Island Rail Road (M1) and on Metro-North's Hudson and Harlem lines (M1A). Final assembly of the M2 cars using Budd or Vickers bodies was completed at GE's Transportation Division in Erie, Pennsylvania. In the late 1980s and early 1990s, the M2 design was licensed by the MTA and ConnDOT to two other companies to produce follow-up series. Tokyu Car produced 54 M4 cars in 1987-1988, and Morrison-Knudsen produced 48 M6 cars in 1993-1995. All cars were equipped with GE 1259 DC motors with a rated output of on all axles. M2 series The M2 "Cosmopolitan" series (numbers 8400-8849) replaced EMU cars dating from the early 1920s to 1954, including the Pullman 4400-series, which were originally manufactured for (and inherited from) the New York, New Haven & Hartford Railroad. As with the cousin M1 series, the M2s accompanied an overhaul of the long-neglected main line and the New Canaan Branch in which longer, high level platforms were introduced along with other infrastructure improvements. The first M2s were accepted for service on April 16, 1973. 144 base order cars were built in 1972-1974, followed by a 100-car option in 1975. These cars had been scheduled for delivery in spring 1971, but were delayed due to technical problems. Aside from the technical differences of the New Haven Line (electrification via overhead