R6 or R-6 may be:
The R6 was a New York City Subway car built in 1935 and 1936. The R6 contract had three separate orders from different manufacturers due to the large order. The R6 separate orders were R6-3 (American Car and Foundry Company), R6-2 (Pullman Standard), and R6-1 (Pressed Steel Car Company). The R6 fleets were almost identical to the R4s which preceded them, except that the R6 had a 2 pane front window compared to the R4's 1 pane window.
The R6's were used for service on the IND exclusively until 1968-9, when many were displaced from the IND by the new R40 and R42 cars, and many were transferred to the East New York Yard of the Eastern Division, and were used on the former BMT J, KK, LL, M, and QJ routes until 1977 when the R6's were retired, and replaced by the R46's.