How was midtown tunnel built?

The Queens-Midtown Tunnel was designed as a twin tube crossing, providing four lanes of through traffic. Excavation on this project proved difficult as crews turned up vast geological variations beneath the East River, creating a costly and exhausting tunneling process. Silt and rock hampered the drilling process often creating dangerous working conditions for the underground "sandhogs". Ground was officially broken on the Queens-Midtown Tunnel the afternoon of October 1, 1936, by then president Franklin D. Roosevelt. The tunnel's final hole-through took place on November 8, 1939, as workers from both the Manhattan and Queens' shoreline met beneath the East River.