then, on april 12th, the confederate general beauregard gave the command to open fire.s is one of the weapons the rebs would have used to bomb the fort. >> this is a 10-inch mortar. which is a small cannon. it's usually used because it has a high trajectory so, it can be used to shoot over the walls of a fortification like ft. sumter. and this is the same type of model that would have fired the first shot of the civil war. so we're standing inside of a casemate here at fort sumter. a casemate is a gun room, so it just would just have one gun inside of it. and as you can see here today, we do have one gun inside of this casemate. this is a 42-pounder. it fired off a 42-pound cannon ball, and is likely that this cannon was here during the first bombardment of the civil war. it might have been active from april 12th to april 13th, 1861, and it might have been firing back at confederate forts in charleston harbor. >> reporter: to give the huge cannons a wider range of fire, they're mounted on wheels. >> each cannon runs on what's called a traverse rail, and that's just how