1862 proposal by Turnbull In 1862, the Government of India asked
George Turnbull, chief engineer of the
East Indian Railway Company, to study the feasibility of bridging the Hooghly River. He had recently established the company's
rail terminus in Howrah. He reported on 19 March, with large-scale drawings and estimates, that: :* The foundations for a bridge at Calcutta would be at a considerable depth and cost because of the depth of the mud there. :* The impediment to shipping would be considerable. :* A good place for the bridge was at Pulta Ghat "about a dozen miles north of Calcutta" where a "bed of stiff clay existed at no great depth under the river bed". :* A suspended-girder bridge of five spans of and two spans would be ideal.
Pontoon bridge In view of the increasing traffic across the Hooghly river, a committee was appointed in 1855–56 to review alternatives for constructing a bridge across it. The plan was shelved in 1859–60, to be revived in 1868, when it was decided that a bridge should be constructed and a newly appointed trust vested to manage it. The
Calcutta Port Trust was founded in 1870, The bridge was then 1528 ft long and 62 ft wide, with 7-foot wide pavements on either side. but was formed by riveting the whole structure. It consumed 26,500 tons of steel, out of which 23,000 tons of high-tensile alloy steel, known as Tiscrom, were supplied by
Tata Steel. The main tower was constructed with single monolith
caissons of dimensions 55.31m× 24.8m with 21 shafts, each 6.25 metre square. The Chief Engineer of the Port Trust, Mr. J. McGlashan, wanted to replace the pontoon bridge, with a permanent structure, as the present bridge interfered with north–south river traffic. Work could not be started as World War I (1914–1918) broke out. Then in 1926 a commission under the chairmanship of Sir R. N. Mukherjee recommended a suspension bridge of a particular type to be built across the River Hoogly. The bridge was designed by one Mr. Walton of M/s Rendel, Palmer & Tritton. The order for construction and erection was placed on
M/s.Cleveland Bridge & Engineering Company in 1939. Again World War II (1939–1945) intervened. All the steel that was to come from England were diverted for war effort in Europe. Out of 26,000 tons of steel, that was required for the bridge, only 3000 tons were supplied from England. In spite of the Japanese threat, the then (British) government of India pressed on with the construction. Tata Steel were asked to supply the remaining 23,000 tons of high tension steel. The Tatas developed the quality of steel required for the bridge and called it Tiscrom. The entire 23,000 tons was supplied in time. The fabrication and erection work was awarded to a local engineering firm of Howrah: the
Braithwaite, Burn & Jessop Construction Co. The two anchorage caissons were each 16.4 m by 8.2 m, with two wells 4.9 m square. The caissons were so designed that the working chambers within the shafts could be temporarily enclosed by steel diaphragms to allow work under compressed air if required. While muck was being cleared, numerous varieties of objects were brought up, including anchors, grappling irons, cannons, cannonballs, brass vessels, and coins dating back to the
East India Company. The job of sinking the caissons was carried out round-the-clock at a rate of a foot or more per day. ==Description==