HH was the last of the letters assigned to original routes of the Independent Subway System

Independent Subway System

The Independent Subway System , formerly known as the Independent City-Owned Subway System or the Independent City-Owned Rapid Transit Railroad, was a rapid transit rail system in New York City that is now part of the New York City Subway...

 of the New York City Subway

New York City Subway

The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority, a subsidiary agency of the Metropolitan Transportation Authority and also known as MTA New York City Transit...

 in the 1930s. It was designated as the dedicated service letter of the IND Fulton Street Line

IND Fulton Street Line

The IND Fulton Street Line is a rapid transit line of the IND Division of the New York City Subway, extending from the Cranberry Street Tunnel under the East River through all of central Brooklyn to a terminus in Ozone Park, Queens. The IND Rockaway Line branches from it. It forms part of the A...

 in Brooklyn

Brooklyn

Brooklyn is the most populous of New York City's five boroughs, with nearly 2.6 million residents, and the second-largest in area. Since 1896, Brooklyn has had the same boundaries as Kings County, which is now the most populous county in New York State and the second-most densely populated...

.

The letter was intended to be used for a Fulton Street local, to run from Court Street, a stub-end station in downtown Brooklyn, to the future Euclid Avenue

Euclid Avenue (IND Fulton Street Line)

Euclid Avenue is an express station on the IND Fulton Street Line of the New York City Subway. Located at the intersection of Euclid Avenue and Pitkin Avenue in Brooklyn, it is served by the A train at all times, and the southern terminal for the C train, at all times except late nights...

 station near the border with Queens

Queens

Queens is the easternmost of the five boroughs of New York City. The largest borough in area and the second-largest in population, it is coextensive with Queens County, an administrative division of New York state, in the United States....

. The service, to be designated HH (the double letter denoting a local train) was to provide local service on the Fulton Street Line, with express service on the 4-track line provided by express trains through routed from Manhattan

Manhattan

Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...

.

When service on the Fulton Street Line began on April 9, 1936, the Manhattan trains provided the local service instead, and the HH ran only as a one-stop shuttle to connect Court Street with Hoyt–Schermerhorn Streets, where connections with other lines could be made. Service between these two stations, which were only three blocks apart in distance, was discontinued on June 1, 1946.

The Court Street station is now the site of the New York Transit Museum

New York Transit Museum

The New York Transit Museum is a museum which displays historical artifacts of the New York City Subway, bus, commuter rail, and bridge and tunnel systems; it is located in a decommissioned Court Street subway station in the Brooklyn Heights neighborhood of New York City...

. The tracks leading to the station are still operable and are used to move trains to and from the exhibit.