At the time of South Carolina's secession, there were three Federal forts in Charleston Harbor: Fort Moultrie, Fort Sumter, and Castle Pinckney, all of which were under the command of Major Anderson. Castle Pinckney was lightly manned and largely abandoned (it has trees growing out of it today), and Fort Sumter was barely finished and mostly occupied by construction workers. The main Federal garrison was in Fort Moultrie, which was considered largely indefensible from a Confederate attack (unlike Fort Sumter, which is on an artificial island out in the middle of Charleston harbor, Fort Moultrie is at one end of an inhabited-and in 1861, Confederate-controlled-island, and its landward defenses were fairly pathetic). The obvious course of action for Major Anderson was to move to Fort Sumter, so, immediately after secession, the South Carolina government detailed three patrol boats to guard Fort Sumter to prevent this.
Now, IOTL, Major Anderson managed to evacuate Fort Moultrie in the dead of the night, and slipped past the South Carolina guard boats under cover of darkness. But what if he had been unsuccessful, and the South Carolina boats had forced the Fort Moultrie garrison to either land in Charleston harbor or simply turn back to Fort Moultrie (in which case they would most likely have surrendered, like pretty much every other Federal fort did). For that matter, what if South Carolina had simply assigned a tighter patrol and Major Anderson had not attempted to relocate (which again, would likely have led to Fort Moultrie surrendering). How might the opening stages of the Civil War have gone without Fort Sumter being a thorn in the Confederacy's side?
Now, IOTL, Major Anderson managed to evacuate Fort Moultrie in the dead of the night, and slipped past the South Carolina guard boats under cover of darkness. But what if he had been unsuccessful, and the South Carolina boats had forced the Fort Moultrie garrison to either land in Charleston harbor or simply turn back to Fort Moultrie (in which case they would most likely have surrendered, like pretty much every other Federal fort did). For that matter, what if South Carolina had simply assigned a tighter patrol and Major Anderson had not attempted to relocate (which again, would likely have led to Fort Moultrie surrendering). How might the opening stages of the Civil War have gone without Fort Sumter being a thorn in the Confederacy's side?