The Clark Street Tunnel carries the 2 3 trains of the New York City Subway under the East River between the boroughs of Manhattan and Brooklyn. It was opened for revenue service on Tuesday, April 15, 1919, relieving crowding on the Joralemon Street Tunnel and providing passengers with a direct route to travel between Brooklyn and the west side of Manhattan. It is about 5,900 feet long, with about 3,100 feet underwater.
Construction of the tunnel began on October 12, 1914, using a tunneling shield in conjunction with compressed air. The tunnel was designed by civil engineer Clifford Milburn Holland, who would later serve as the first chief engineer of the Holland Tunnel.