As built, the first 28 locomotives in the 1926 order formed semi-permanently coupled pairs grouped in three classes.

The third, class BB3, was AC powered and built for the Long Island Rail Road's electrified freight operation on the Bay Ridge Branch.

In 1934 a follow-up order of 14 locomotives were built as single unit class B1 for the expanding main line AC electrification system.

[1] Most of the B1 fleet spent its time shuttling trains around Sunnyside Yard or between there and Penn Station.

As passenger traffic decreased in the 1950s and 1960s the need for dedicated electric switchers diminished[1] with only the Sunnyside B1s surviving into the Penn Central era.