During the 1930s, New York City began to explore various schemes to handle the automobile traffic and congestion in Lower Manhattan. Robert Moses, then Chairman of the Triborough Bridge Authority, proposed a massive suspension bridge linking the lower tip of the Manhattan at the Battery to Brooklyn at Red Hook. This scheme was massively unpopular in the eyes of New Yorkers, most prominently First Lady Eleanor Rooseveldt, who believed the bridge would be detrimental to the overall aesthetic of New York City. Nonetheless it took an executive order by President Rooseveldt to over-rule Moses' plans for a bridge and allow the tunnel project to proceed in 1939. The City employed its chief engineer Ole Singstad, designer of the Lincoln Tunnel, to oversee the Tunnel's development. The project was begun on October 28th 1940, but delayed from 1941 until 1946 because of due to material shortages during World War Two. By this time Moses had taken control of the Tunnel as it now fell under the jurisdiction of the newly formed Triborough Bridge and Tunnel Authority. He fired Singstad and replaced him with Ralph Smillie who, after a faulty Moses-inspired redesign, completed Singstad's design. The tunnels opened on May 25th, 1950 and remain an important part of New York's transportation network to this day.
Although the Tunnels (consisting of 4 lanes of traffic held in two tubes) are in themselves a major feat of engineering, the system also includes 4 major above-ground structures: the Battery Parking Garage, a ventilator building off of Governor's Island, and Portal/ Ventilator Buildings at both the Manhattan and Brooklyn Sides. At 9,117 feet the tunnel is the longest of its kind in North America. All of the above ground features of the system are designed in a Streamline Moderne aesthetic.
1940-1950. (5 year hiatus due to World War Two)
The Brookyln-Battery Tunnel System was at the time of its construction the longest continuous underwater tunnel in the world; today it remains the longest in North America. The Tunnel was designed by engineer Ole Singstad, Chief Engineer for New York City and utilizes an innovative system by which a trench is burrowed into the river bed with cast-iron rings being the principal structural component of the tunnel. The road bed is then laid into the 31 foot diameter wide tunnel. Essential to automobile tunnels is ventilation, and the ventilation towers of the Tunnel are capable of exchanging the entire volume of air in the tunnels every 90 seconds. The above-ground structures which house ventilator equipment are built entirely of reinforced concrete (with the exception of the Garage which includes glass-brick window-walls).
In the early to mid decades of the 20th century, American society was being rapidly altered by the proliferation of automobiles. Personal transportation revolutionized not just the urban fabric of cities, but also they way the people thought about them leading to the rapid growth of suburban areas - and the means to get to them. Anticipation of the demand to live in Manhattan but live in the suburbs of Long Island led to the development of the Brooklyn-Battery Tunnel.
The buildings and tunnels are a product of and for the Automobile Age. The structures associated with the tunnels (particularly the Garage and Governor's Island Ventilator) are built in the Streamline Moderne style, a later offshoot of the eclectic Art Deco movement. This style is particularly apropos in that it emphasized depicting movement and transportation in buildings in an historical moment when both automobiles and air travel where becoming more accessible to a wide segment of the American public. By building a tunnel instead of a bridge, views of lower Manhattan were preserved.
The Brooklyn Battery Tunnel System is a grand feat of urban engineering and architecture, as much so as the better known bridges of New York City or the aqueducts of antiquity. The story of its construction is a rich part of the history of New York City and involved many if not all of the historical figures associated with construction in New York during the 1940s. Still serving its intended use exquisitely, it stands as a monument of the industriousness of mid-twentieth century America. The Manhattan Portal continues to be the last image of Manhattan thousands of Brooklynites see every work day.
"President Breaks Ground for Tunnel" - NY Times Archive October 29,1940.
http://select.nytimes.com/gst/abstract.html?res=F20714FE3C5C10728DDDA00A...  Ingraham, Joseph C. "Brooklyn Tunnel Costing $80,000,000.00 opened by mayor" - NY Times Archive May 26th, 1950. http://select.nytimes.com/gst/abstract.html?res=F30C13FC3B5F177A93C4AB17...  Armagnac, Alden P. "Sandhogs' toughest job" - Popular Mechanics Sept.1947, Google Books. http://books.google.com/books?id=miQDAAAAMBAJ&pg=PA82&dq=popular+science... 
MTA Webpage: http://www.mta.info/news/stories/?story=66 
Caro, Robert A., The Power Broker: Robert Moses and the Fall of New York, New York: Knopf, 1974.
Depicted item: Short MTA produced movie on the Tunnel, source: MTA Info