In 1960, with the delivery of the first R27 class cars for the BMT, the New York City Transit Authority (TA), which had become the operator of the combined system in 1953, began the introduction of letters for BMT services in anticipation of integrating the BMT and IND operationally. The last IND letter used was "H", and the letter "I" was skipped as being too similar to the number "1". The BMT Eastern Division services got the letters J, K, L and M. The BMT Southern Division services were designated N, Q, R and T. P was for some reason skipped over, and while one theory says this was because it might lend itself to bathroom humor, the letter's undesirability for this reason would seem to be disproven by the fact that the letter was later proposed for an emergency line that would replace Long Island Rail Road service to Penn Station in the event of a strike, and the fact that other cities like San Francisco use the letter. A more likely theory suggests that it was originally planned for the last segment of Culver service to Manhattan, which was cut back to a shuttle permanently in 1959, right before the letters were introduced. "S" was still reserved for "Special" and "SS" began to be used for shuttles.