The Monitor and the Merrimack were re-created in models one third of their actual size, and the battle scenes between them were filmed in the big tank at Pinewood Studios, England.
Full scale cannons on the ironclads sets and sailing ships were made of fiberglass, designed and molded by armorer Roger Ragland. The molds were pulled from original guns at the Confederate Naval Museum Columbus, Georgia. In total, there were seven guns made: one Brooks Rifle Cannon, two eleven-inch Dahlgrens, and four nine-inch Dahlgrens, as well as three thirty-two pounders from Raglands earlier Glory (1989). A total of ten guns were used in all scenes.
If you watch carefully during the opening credits, you will see a horse fall and the rider strike his head on the ground. That was not an effect, but rather a real event where the rider suffered a head laceration and required transportation to a local hospital. There were multiple cameras used for that shot, and they continued to roll for about twenty seconds to capture the explosion effects before medics were clear to assess and treat the rider.
In a 2017 interview, Alex Hyde-White mentioned that most of the film's extras were Civil War re-enactors who contributed their own costumes, weapons, and props.
Filmed mostly in Richmond Va. The fire scene was filmed in warehouses by the James River. All the cannonballs were made of plastic. If you watch, you can see some of them bouncing off the side. The ball scene was filmed at a local plantation. Most of the extras were hired by a newspaper listing calling all local reenactors that were bussed out to the sites.