The first subway in America was not a train, but a pneumatic people mover! Opening for business in 1870, the subway worked on the same principle as the pneumatic tubes we use at a drive-through bank. Giant fans at either end provided pressure to blow a carriage through Manhattan.
For a fare of two bits per passenger– all of which was donated to a charity for soldiers' orphans– twenty guests at a time could take a ride on the pneumatic carriage. The custom-built, fifty-ton blower was situated in an adjacent chamber, separated from the waiting area by a long corridor. The Æolor blower was twenty-one feet high, sixteen feet long, and thirteen feet wide, and it contained two colossal lengthwise paddles which rotated to draw air in one side and out the other. The magnificent blower was outfitted with a special set of adjustable baffles which allowed her to switch from suck to blow without reversing rotation. By tapping a telegraph wire, the conductor signaled the boiler engineer to engage the 100 horsepower steam engine. Atmospheric pressure increased by "a few grains per inch," pressing the carriage into the tunnel as the air rushed to escape through the vent at the far end.
Financial problems led to the closing of the carrier in the 1870s. The tunnel was sealed until 1912, when it was reopened for the installation of an electric subway line. Link