This chart from the Officials Records of the Union and Confederate Navies diagrams the U.S. Navy assault on Fort Sumter on April 7, 1863.

The gunboats sailed into the Stono a little farther every day, shooting at troops on James Island before slipping back out to sea.

It began in the fall of 1862 and continued into the winter of 1863, the Yankees growing more brazen each week.

The Union Navy, it seemed, was pushing the limits of its reach into South Carolina, and in the process preventing the Confederates from fortifying the riverbanks.

The most troublesome, and bold, of these ships was a converted river steamer called the Isaac P. Smith. Its captain, Lt. F.S. Conover, allowed his bored crewmen to pass the time by taking target practice on houses along the river -- or any person who wandered into view.

Once, the Isaac P. Smith's crew even landed a boat at an abandoned plantation on Johns Island and drew a picture of a man on a carriage house. For days afterward, the sailors amused themselves by shooting at their crude artwork.

When Gen. P.G.T. Beauregard got wind of this behavior, he decided to make an example of the Isaac P. Smith.

Quietly, Beauregard ordered some men to move several heavy guns from the peninsula to James Island. These guns were hidden near the riverbank on Thomas Grimball's plantation -- some later would claim they even camouflaged one with a bale of hay. At the same time, other guns were moved to Johns Island. The Confederates stowed two guns inside the carriage house sporting the Yankee artwork.

The trap was set by Jan. 29, 1863, but the Confederates would have to lie in wait for more than a day to spring it.

Troops spotted the Isaac P. Smith steaming up the Stono on Friday afternoon, just as it passed Grimball's plantation. The boat was so close to shore that the Confederates could identify the lookouts on each of the boat's three masts.

But the crew of the Union gunboat did not see the Confederates in time.

Capt. John H. Gary watched the ship creep along less than 100 yards offshore and waited for his moment. When Gary saw what he decided was the best shot, he ordered his men to open fire.

The first shot ripped through the Isaac P. Smith's timbers, sending Union sailors scampering around the deck. They had been taken completely by surprise, but, within minutes, regained their composure enough to retaliate. The gunboat returned fire.

For a moment it looked as if it would turn into a real fight. The Yankees took out one of the Confederate guns with a single shot. But soon, the troops on Johns Island got off three good shots in a row, one of which took out the Isaac P. Smith's engine. A second later, the ship belched white steam from its stack and Conover raised the white flag of surrender.

It was one of the first times in history that a warship had surrendered to field batteries.

Blockade runners

Between the surrender of the Isaac P. Smith and the Palmetto State's attack on the blockade a day later, it seemed Charleston had improved its naval defenses. But, in fact, Beauregard was deeply worried.

Every intelligence report that landed on his desk that winter suggested the Union Navy was planning a major assault on Charleston. On Tuesday, Feb. 17, The Mercury published a report from Savannah that claimed Yankee troops from Hilton Head were overheard discussing plans to attack Charleston the following Sunday.

The newspaper ominously noted there were an estimated 50,000 troops on or around Hilton Head.

Beauregard responded immediately. The next day, The Mercury printed a letter from the general warning of a possible attack and stressing his hope that "all persons unable to take an active part in the struggle" would get out of town.

The entire city was on edge by the weekend. When a Yankee gunboat approached Sullivan's Island on Saturday, locals feared the attack was underway. But troops on the island quickly spotted a white flag flying from the Flambeau. It turned out the boat was simply trying to deliver mail for the captured crew of the Isaac P. Smith.

Charleston was quiet for weeks after that, but the dread of impending attack was never far from anyone's mind. The next scare came March 12, when the city was awakened by the sound of heavy firing in the harbor. For two hours the shooting continued unabated, leading some to believe the Yankees were coming.

As it turned out, the first shots were a test of battery signals in the event of an attack. But someone didn't get the memo and soon batteries around the harbor had joined the shelling. One shot damaged a newly occupied house on Sullivan's Island.

Luckily, it was the only casualty of the day.

As winter thawed into spring, Beauregard divided his time between the city's defenses and arguing arcane points of law. Several Southern lawyers maintained that when an enemy fleet wants to blockade a harbor, they must give ample notice of their intent. These attorneys convinced the general that if the fleet is dispersed for even a brief amount of time, the legal process has to begin again.

Beauregard tried to use this quaint law of war to clear the channel of Yankee ships. But the U.S. Navy refused to budge -- or concede that the blockade was disrupted in the attack by Charleston's ironclads.

On March 7, The Mercury published a letter sent to the newspaper by officers of the blockading fleet. It said, "No vessels were sunk and none set on fire" during the Palmetto State and Chicora's attack.

They claimed the Mercedita and the Keystone State were slightly damaged, but that was all. There had been no break in the blockade, they said. The two sides may have been wary of engaging in a naval battle, but they were more than willing to snipe at each other in the press.

The war of words did not distract Beauregard so much that he failed to notice the build-up of Union forces off the coast. It seemed the number of ships joining the blockade increased slightly every week.

Despite this ever-growing fleet, it seemed that more blockade runners than ever were reaching the city, and the economy was showing signs of life. On March 10, W.B. Ryan reported selling 15 slaves for an average price of $992 -- which included $1,810 for one 20-year-old woman. Within a week, the steamer Ruby arrived from Nassau, selling its cargo for a substantial profit.

The next day, March 18, the British steamship Calypso outran blockaders and dodged heavy shelling to reach the wharf in Charleston with her cargo of contraband. But the next ship would not be so lucky.

Around 1 a.m. on Thursday, March 19, the British steamer Georgiana sailed within sight of the South Carolina coast, carrying medicine, dry goods and six pieces of field artillery for Charleston. Off Dewees Island, the Georgiana passed a schooner and a steamer -- both blockaders -- but neither spotted her.

That luck would not hold. A few minutes after slipping by the two unsuspecting ships, another blockader spied the Georgiana and opened fire with deadly efficiency. One shell exploded under the ship's stern, taking out her rudder.

To escape capture, the Georgiana's captain ordered his crew to run the ship aground on Long Island (modern-day Isle of Palms). When the ship hit the beach, the crew flooded her to keep the Union Navy from taking the ship or its cargo.

Charleston, desperate for supplies, had just lost another cache that was almost within reach.

A reluctant attack

On March 30, The Mercury reported there had been some "unwanted activity" by the enemy off the coast. In the last week, pickets had spotted a fleet of 21 ships in the North Edisto River. Among the boats there were at least four turreted ironclads.

Over the weekend, "intelligence reports" noted that a gunboat and three transport ships had approached Cole's Island at the mouth of the Stono and landed some 200 troops there. It appeared the Yankees were preparing to attack.

Charleston didn't realize it at the time, but the Union fleet's heart wasn't in it.

Rear Adm. Samuel F. DuPont had spent the winter preparing to attack the city but still didn't think he was ready. He had received word that Beauregard was reinforcing the harbor and DuPont had considerable respect for the general's military prowess.

There were rumors that the entrance to Charleston Harbor was lined with mines, and it frustrated DuPont that he could not confirm this bit of intelligence. And if that weren't enough, he was not particularly happy with his ironclads.

After putting the ships through a series of tests, DuPont had concluded that the Patapsco, Passaic and Nahant were slow and quick to break down -- similar to the problems that afflicted Charleston's own ironclads. Worst of all, DuPont had decided these ships were no match for the forts protecting Charleston.

But officials in Washington insisted that he press on with his plans, and DuPont was not a man to ignore orders.

On Tuesday, April 7, The Mercury declared "The Hour At Hand." The newspaper reported that nine ironclads -- "eight turreted Monitors and the Ironsides" -- as well as 30 wooden ships had appeared off the bar the day before.

"At all events, their movements were such as to induce the anticipation that the thunders of conflict will be heard before our next issue shall meet the eyes of our readers," Robert Barnwell Rhett Jr. wrote.

Although The Mercury repeated rumors that ground troops would once again descend on James Island, this was largely a naval battle. Around 2:30 that afternoon, the ironclad Weehawken began moving toward Fort Sumter, the Union fleet spread out behind it. The battle was on.

The Confederates would not waste any ammunition on errant shots. Just after 2 p.m., the lead ship had been about 3,000 yards out, but they waited nearly an hour later before Charleston reverberated under "the dull detonation" of the first shot from Fort Moultrie. The shot was answered by immediate fire from the U.S. Navy ironclads, each shot leaving white puffs of smoke hovering over their turrets.

At 3:10, Fort Sumter joined the fray, opening her guns on the ironclads as batteries on Morris and Sullivan's islands provided additional firepower.

No matter how much the Confederates fired at the ironclads, the Navy ships kept coming. As the turreted ships approached shore, they fired 15-inch rounds at Moultrie and some of the smaller batteries. But most of their efforts were directed at the east face of Sumter.

At 4:30, the battle was still "fierce and general," and Charleston Harbor was blanketed in smoke. The ironclads shifted their position, always turning their turrets on Sumter.

Moultrie's guns were trained on the closest ironclad, and they made contact with deadly efficiency. But when one of the ships fired back, the shell took out the fort's flagstaff and killed a private named Lusby. Fort Sumter lost no men, but one shot sent a shower of bricks onto Sgt. Faulkner and the men of Company B. A few soldiers were injured in the melee, and another shot tore the fort's Confederate flag.

Aboard the New Ironsides, DuPont felt helpless. The ship had taken an estimated 93 hits and, through the firing, the admiral could not signal the other boats. But he knew the battle was lost. He ordered the ship to begin steaming south, firing a few parting shots at Sumter as they went. The ironclad Keokuk followed and by 4:45, the shooting began to taper off.

Aboard the Weehawken, Capt. John Rodgers felt his ship shudder from one shot and thought it was one of the underwater mines that DuPont had warned them about. Worried that he might sink, Rodgers ordered a retreat. Behind him, the fleet fell apart.

The ironclad Keokuk would become the battle's largest casualty. As the New Ironsides came up alongside the boat, Capt. A.C. Rhind told DuPont the boat was sinking. It was abandoned just off Morris Island, where it sank the next morning.

Over the next week, equipment and furniture from the ironclad washed up on the beach at Morris Island. Confederates collected some of the debris and ultimately decided to mount a dangerous expedition out to the ship. Under the nose of the blockade, the Southerners stripped the Keokuk of an 11-inch gun, which was ultimately mounted at Fort Sumter.

That was the final irony of the battle. Not only had Charleston repelled one of the most powerful naval squadrons ever assembled, they could now use one of the United States' own guns against it.

Beauregard and his troops had bested the Union forces once again and, after months of tension, Charleston could relax somewhat.

But this, as it turned out, was only the opening salvo in the coming siege.

Next: Showdown on Morris Island