What does R10 stand for? 

R10

The R10 was the first post-war New York City Subway car class built by the American Car and Foundry Company in 1948 and 1949. The cars were nicknamed Thunderbirds. The R10s were mainly assigned to the IND Eighth Avenue Line's A train from 1948 thru early 1978. The R10 cars were numbered 1803–1852 and 3000–3349. They first ran in service on the A service on November 20, 1948. They were initially assigned to the Eighth Avenue Express A train where they remained for almost 30 years and became synonymous with that route. Initially Fifty cars were transferred to the BMT Eastern Division in 1954 to help familiarize crews with SMEE equipment in anticipation of the arrival of the R16 cars. Then twenty cars were returned to the IND for the opening of the IND Rockaway Lines during 1956, leaving only thirty R10 cars from 3320-3349 operating on the BMT Eastern Division until 1961 when new R27/30's cars were delivered to the BMT Lines of the New York City Transit System.

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