Removal of Hell Gate rocks

Then in 1851, the U.S. Army Corps of Engineers, led by General John Newton, began to do the job, in an operation which was to span 70 years.

[4] The blast has been described as "the largest planned explosion before testing began for the atomic bomb",[4] although the detonation at the Battle of Messines in 1917 was larger.

Dutch explorer Adriaen Block, the first European known to have navigated the strait, described it in his journals during his 1614 voyage aboard the Onrust.

[7] Because explorers found navigation hazardous in this New World place of rocks and converging tide-driven currents (from the Long Island Sound, Harlem River strait, Upper Bay of New York Harbor, and lesser channels, some of which have been filled), the Anglicization stuck.

In 1832, the New York State legislature was presented with a petition for a canal to be built through Hallet's Point, thus avoiding Hell Gate altogether.

Underwater blasting was in its infancy, and early technology was of limited use; cans of powder were placed against the side or top of a rock and detonated with a battery.

Ebenezer Meriam had organized a subscription to pay Maillefert $6,000 to, for instance, reduce "Pot Rock" to provide 24 feet (7.3 m) of depth at low-mean water.

[10] By then Maillefert had cleared the rock "Baldheaded Billy", and it was reported that Pot Rock had been reduced to 20.5 feet (6.2 m), which encouraged the United States Congress to appropriate $20,000 for the Army Corps of Engineers to further clear the strait, but the money was soon spent without appreciable change.

[11] With the main shipping channels into New York through The Narrows into New York Harbor silting up with sand due to littoral drift, thus providing ships with less depth to travel through, and a new generation of larger ships coming online – epitomized by Isambard Kingdom Brunel's SS Great Eastern, popularly known as "Leviathan" – New York began to be concerned that it would start to lose its status as a great port if a "back door" entrance into the harbor was not created.

[13] An advisory council recommended in 1856 that Hell Gate be cleared of all obstacles, but nothing was done, and the Civil War soon broke out.

It was first used on Diamond Reef in the spring of 1869; a number of holes were drilled into the rock, into which 30-to-35-pound (14 to 16 kg) charges of nitroglycerin were inserted.

A wood cofferdam was fastened to the rocks, and the water was pumped out about to accommodate a shaft; work was then suspended because its funding had run out.

A chain of explosions was planned which would minimize vibration in nearby Astoria, and on Ward's and Blackwell's Islands.

One lesson learned from the detonation was that moderate charges, confined in rock and cushioned by water, would not damage surrounding objects.