The first set of R21s was placed in service on the 1 train on November 7, 1956, replacing most of the IRT "high-voltage" type cars.

The R62A fleet started replacing the R21s in the 1980s, and their final day in revenue service was on December 30, 1987.

The majority of the fleet was scrapped, but some R21s have been set aside for preservation over the years, including: As of 2016, two other R21s survive as work cars, including: Car 7267 (renumbered G7267) is currently at Concourse Yard coupled up to R17 6895 (renumbered 36895) and is classified as a garbage motor.

In 2009, both cars were stripped of parts, such as sash windows and rollsigns, and are now awaiting scrapping.

[8] Media related to R21 (New York City Subway car) at Wikimedia Commons