The siege of Charleston began in early April, 1863. The most powerful armada of the Civil War — or indeed of any war to that date — had assembled at Port Royal, and when it arrived in Charleston, it consisted of the deadliest ships of the Union Navy: seven ironclad monitors, flat ships with “cheese box” turrets on top (the Passaic, Montauk, Patapsco, Weehawken, Nantucket, Catskill, and Nahant); the experimental Keokuk; the New Ironsides, a large armored frigate; and other vessels. The New Ironsides weighed 3,500 tons; it carried 16 Dahlgren guns and two Parrott rifles. It was the heaviest artillery afloat — indeed, “the most powerful battleship in the world.” The Keokuk was an ironclad but had five feet of slanting hull above the water. The Courier reported that “the Abolitionists [have] been gradually marshalling their naval forces in front of the harbor.” John Johnson wrote in “The Defense of Charleston Harbor”: “In point of both armament and power of resistance, it was to be the most formidable naval attack hitherto made in this or any other country.” In the great naval battle at Sebastopol in 1854-55, during the Crimean War, the British fleet had less firepower.

Major Gen. Pierre G.T. Beauregard had established excellent defenses for the city: obstructions in the harbor, 77 guns and cannons of various sizes, mines, torpedoes and well-placed fortifications described by one Union officer as “a porcupine’s quills turned outside in.” (Two of the Columbian cannons, which constituted the bulk of Sumter’s artillery firepower in 1863, are today at White Point Gardens.)

The harbor was full of rope obstructions designed to catch the propellers of the Union ships and mines to blow them up. The Confederate command had taken full advantage of the peculiar geography of Charleston Harbor. The Palmetto State and the Chicora, two ironclad steam rams similar to the famous Merrimac, were on hand. Beauregard had even given the order for the creation of the first submarines to be used successfully in warfare.

The Confederacy did not have much of a navy; torpedo boats and submarine warfare were its only real hope on the sea. The first submarine-type vessel, David, was semi-submersible with a torpedo attached to a pole 30 feet in length. It was to be used successfully against the New Ironsides in October. Similar boats, called Little Davids (because they were designed to fight the Union Goliaths), were soon in production.

The Union fleet’s attack on Fort Sumter began 150 years ago, on the afternoon of April 7, 1863, when Rear Adm. Samuel DuPont, nephew of the illustrious Delaware powder maker, ordered his powerful fleet to enter Charleston harbor. DuPont had grave doubts about the siege. Unlike others, who admired the monitors, DuPont was a sailor of the old wooden navy. He had little faith in the newfangled monitors, doubting their ability to win a decisive battle with a fort.

The Navy Department, DuPont said, had a “morbid appetite” to capture Charleston, and he was threatened with being relieved of his command if he did not attack. The armada was led by the monitor Weehawken, pushing a large raft to explode torpedoes, followed by three other monitors, the New Ironsides, and then four more monitors. The Passaic was under the command of Percival Drayton, the Charleston native whose brother was a Confederate officer.

They sailed into the harbor believing they could successfully storm one of the great fortresses of the South.

Robert N. Rosen, an attorney, is the author of “A Short History of Charleston” and “Confederate Charleston.”