Anderson had about 80 men, Beauregard thousands. There were very few casualties.
Charleston Harbor was the tinderbox of the Civil War, but Fort Sumter was nothing special. Work began on the fort thirty years before the war, and, thanks to low Federal spending, it was still unfinished and already obsolete by 1861. The mainly brick Fort rested on an artificial island (New England granite) and could mount about a hundred guns, some out of apertures (casemates) and some firing over the wall (en barbette, in the fancy language of fortifications). The Fort could mount these guns, but lacked enough men to man them: the whole garrison of Charleston Harbor consisting of two companies of artillerymen (only 85 men) under the command of Major Robert Anderson. With the political temperature rising steadily after Lincoln's election and South Carolina's secession, Anderson was between a rock and a hard place. There was no way he could defend all the fortifications (Fort Sumter, Fort Moultrie, Castle Pinckney, Fort Johnson) and was afraid the South Carolinians would overwhelm his forces in the weak Fort Moultrie. So, on the night of December 26, 1860, the US troops rowed through a dark and stormy night to Fort Sumter.
The South Carolinians were outraged, and it suddenly looked as if there would be a fight. After all, if Anderson intended to hand over the fort, why had he moved to Sumter? The State troops began to build batteries, collect powder and guns, and tried to isolate the Fort. Meanwhile, Anderson had to persuade the civilian workmen to stay and help finish the fort and mount the guns. Over the next three months, Anderson's men mounted 47 guns (26 on top of the wall, 21 in protected casemates) while Pierre GT Beauregard cajoled the feisty South Carolinians into building fewer useful batteries, rather than having everyone build their own.
Negotiations between South Carolina and Major Anderson were going nowhere. Anderson looked for guidance from Washington, but the Buchanan Administration didn't want to take the responsibility. The Secretary of War, Virginian John Floyd, had resigned and finding anyone to make any decision was virtually impossible. Eventually the Navy sent an unarmed merchant ship (considered less provocative) the Star Of The West, with supplies and 200 reinforcements. In Confederate eyes this was reinforcing a foreign garrison on their soil and, therefore, and act of war. On January 9, the Confederate fired on the Star, turning her away, leaving the supplies and reinforcements undelivered. Anderson, not wanting to be provocative, refused to fire on the Confederate batteries. Over time, Anderson's position weakened, as he relied on the generosity of others to feed his men. Whenever they chose, the Charlestonians could cut off his food supply.
The South Carolinians wanted a decision from Anderson sooner rather than later because they knew what Lincoln's orders would be: stand fast. Anderson continued to hope for a peaceful outcome to the tense situation. He supported slavery, coming from a slave state (Kentucky), but his loyalty to the Union was stronger than anything else. He would not surrender his country's property.
On March 4, 1861, Lincoln was inaugurated, and the pace picked up. In a firm but conciliatory inaugural address he said he would uphold the national authority. The Government, he said, would not assail anyone, but neither would it consent to a division of the Union. "The power confided to me will be used to hold, occupy, and possess the property and places belonging to the Government." Lincoln plainly meant to hold Fort Sumter. But what could he do? Inexperienced in Washington, knowing little of the sea or naval matters, it took time for the new Administration to make a decision. By April 4 Lincoln believed that a relief expedition was feasible and ordered merchant steamers, protected by warships, to carry "subsistence, and other supplies" to Anderson. He also notified Governor Francis W. Pickens of South Carolina that an attempt would be made to resupply the fort. After debate - and some disagreement - the Confederate cabinet telegraphed Beauregard on April 10 to fire on Fort Sumter if absolutely necessary to prevent reinforcement.
On April 11, Beauregard demanded Anderson surrender Sumter. Anderson refused, but said he would be starved out in a few days anyway. Beauregard then asked the major precisely when he would be forced to evacuate the fort. Anderson carefully considered his reply and said that he would leave by noon, April 15, unless before that time he should receive either instructions from Washington or additional supplies.
That wasn't fast enough for the Confederates. At 3:20 a.m., April 12, they informed Anderson that their batteries would open fire in one hour. After an hour and ten minutes, Capt. George S. James, commanding Fort Johnson's east mortar battery, ordered the firing of a signal shell. Within moments, Edmund Ruffin of Virginia, firebrand and hero of the secessionist movement, touched off a gun in the ironclad battery at Cummings Point. By daybreak batteries from around Charleston Harbor were assailing Sumter.
If Anderson was short of food, he was also short of powder and fuses. He waited three hours, until after daylight, to return fire. Captain Abner Doubleday fired the first return shot. It missed, sailing high over the Iron Battery on Cummings Point. Of the 47 guns that had been readied, most never got into the fight. Nine or ten casemate guns returned fire, but by noon only six remained in action. Unsurprisingly, the Federal bombardment never did much damage. Observing the rules of warfare, Anderson and his men weren't firing on the city of Charleston, and were fast finding that solid shot didn't much damage to earthen batteries.
The cannonade continued throughout the night. The next morning a hot shot (cannon balls heated in a furnace to start fires) from Fort Moultrie set fire to the officers' quarters. In early afternoon the flagstaff was shot away. Soldiers braved the shells and fires in the courtyard and retrieved the flag, which they hung out a casemate. About 2 p.m., Anderson agreed to a truce, convinced that help was not coming. That evening he surrendered his garrison. Miraculously, no one on either side had been killed during the engagement, and the Federal soldiers, sheltered in Sumter's brick caverns, suffered only five injuries. Sadly, during the 100-gun salute to the US flag ' Anderson's one condition ' a pile of cartridges blew up from a spark, killing two soldiers. On Sunday, April 14, Major Anderson and his garrison marched out of the fort and boarded ships for transport to New York. They had defended Sumter for 34 hours, until "the quarters were entirely burned, the main gates destroyed by fire, the gorge walls seriously injured, the magazines surrounded by flames."
Civil war, so long dreaded, had begun.