That “subway” tunnel in Brooklyn was never part of the subway but was built by the Long Island RR in 1844; it extended the Atlantic Avenue line east from Flatbush Avenue to the former Fulton Ferry location (now Fulton Ferry Landing) and was part of the LIRR’s original “rail-sail” service to Boston, where passengers would be again ferried from Greenport NY to Stonington CT.
West, not east.