When the U.S. Navy attempted to pass Fort Sumter in April 1863, one feared component of the Confederate defenses were the obstructions and torpedoes anchored between Fort Sumter and Sullivan’s Island. Seven months later and those obstructions still barred the Federals from Charleston harbor. Rear-Admiral John Dahlgren cited them in his assessment of the situation in October of that year. With approval to attempt another run past Fort Sumter, Dahlgren turned to a device designed by John Ericsson named “the obstruction remover” as a potential solution to the problem at hand.
Recall that in the failed attack of April 7, the Federals had used something from Ericsson nicknamed “the Devil” and called “the obstruction remover” in some correspondence. What is not clear IN the correspondence from November 1863 is if the obstruction removers were one and the same. Or if these were similar designations of different devices originating from the same inventor. A Confederate diagram of “the Devil” that washed ashore after the April attack shows chains and hooks suspended from a raft, shaped to fit onto the bow of a monitor:
However, Federal descriptions did mention explosive devices suspended in front of the raft. These devices were intended to be placed upon the obstructions then triggered remotely to blast a path. Descriptions of the obstruction remover tested in November 1863 focus on the explosive device and less so on the raft. Thomas J. Griffin, serving as a technical inspector of ironclads, provided description of the device as tested in November:
This obstruction remover consists of a cast-iron shell, or torpedo, about 23 feet long and 10 inches in diameter, containing 600 pounds of powder. This is discharged by a trigger board placed directly in front and extending the entire length of the shell, adjusted on the plan of a parallel ruler; this board, by being pushed in contact with obstructions, will spring two locks placed equidistant on the torpedo, causing an explosion of the shell. These torpedoes are suspended from rafts carried on the bows of monitors, and held in position forward by two booms, which are firmly secured to the raft; there is also attached to the forward part of the torpedo a series of air vessels, so arranged to cause the explosive powder to be expended in that direction.
When, on November 4, the USS Patapsco went off the gun line for repairs and a replacement Parrott rifle, Dahlgren ordered additional tests of the obstruction remover. Commander T.H. Stevens, of the Patapsco reported two trials were conducted on November 6, “… one of which failed on account of the damaged condition of the powder, we succeeded yesterday in exploding the torpedo designed by Mr. Ericsson.” Griffin offered a detailed examination of the tests:
As this trial was only made to show the effect of the explosion on the monitor, and how much it interfered with the maneuvering of the vessel, it was carried on in deep water. The Patapsco, the vessel on which the trial was made, had, on account of the foulness of her bottom, only a speed of about 3½ knots; with the raft on, I should judge she was not to be driven more than 3 knots; and in making a circuit with the helm hard down, it takes at least half as much more room.
In exploding the torpedo, which was suspended at a depth of 13 feet, the shock was hardly perceptible on the Patapsco, while the body of water displaced and thrown upward to a height from 40 to 50 feet, was really fearful; this body of water was thrown forward, and but a slight quantity of water fell upon the deck of the vessel. The raft was raised about 2 feet at the forward end, but sustained no material injury.
Both Stevens and Griffin considered the the obstruction remover tests successful. However, both offered caution with respect to the maneuvering of the monitors with these devices fitted. Griffin added that the three rafts on hand could be fitted out, save the torpedoes themselves, and set up “for use at short notice.”
The idea of using an explosive device (and a rather large one in this case) to clear obstructions and mines is practical, to say the least. In fact, that basic idea is in use today, on land, in the form of the Mine Clearing Line Charge (MICLIC):
The line charge is a bit more sophisticated, with a rocket pulling a line. The charge is five pounds of C-4 explosive per linear foot. The explosive line is triggered electrically and remotely (not on contact as with the Ericsson device). Bigger boom, to say the least. Principle is the same – the explosion clears mines and obstacles to form a safe path about 25 feet wide.
But in 1863, the Navy didn’t have rockets to put the charge at the necessary point. To bring the Ericsson Obstruction Remover into position, the ironclads would need to navigate the confined and dangerous waters at the mouth of Charleston harbor. Events in mid-November would demonstrate just how difficult that would be, even with Fort Sumter suppressed.
(Citations from ORN, Series I, Volume 15, pages 102-3.)