Montague Street Tunnel

The Montague Street Tunnel is a rail tunnel of the New York City Subway under the East River between the boroughs of Manhattan and Brooklyn, connecting the BMT Broadway Line and BMT Fourth Avenue Line. The R uses the tunnel at all times, the N uses it during late nights, and during rush hours, several W trains per day in each direction use the tunnel.

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. The north tube of the tunnel was holed through on June 2, 1917, and the south tube was holed through on June 20, 1917.

Wikipedia