2303 East Fort Macon Rd, Atlantic Beach, NC 28512
(252) 726-3775

Hot Shot Furnace


Hot Shot Furnace are structures included in the typical defenses of any fort which were used to heat non-explosive cannonballs red hot for the purpose of setting fire to enemy warships, buildings or equipment. The use of hot shot goes back centuries and only ceased when modern armored warships appeared in the world’s navies. Fort Macon’s furnaces were removed long ago by the Army once their usefulness declined. Although the original furnaces were built at a cost of about $300 in the early 1800’s, the modern cost of replicating one is high due to the fact they are free-standing brick masonry structures with special iron racks, grates and braces. However, through the interest and generosity of the Atlantic Beach Merchant’s and Professional Association, a sum of $15,000 has already been donated toward the project.


The use of hot shot represents one of the most unusual and effective defenses possessed by a fort such as Fort Macon in the eras predating modern armored warships. However, the idea of setting fire to enemy ships and equipment can actually be traced back in antiquity where flaming arrows and incendiary compositions such as “Greek Fire” were used in warfare hundreds of years before Christ. Similarly in 54 B.C., heated clay balls were used by the Britons to burn Roman tents and camps. In Classical and Medieval siege warfare, catapults and similar devices commonly hurled fire balls and incendiaries into besieged castles and towns. Then with the invention of gunpowder, cannons came into general use during the Hundred Years War (1337-1453). It was only a matter of time and logical thought that efforts would thus be made to modify cannon projectiles to cause fires. Perhaps the first successful use of hot shot was by King Stephen Bathory of Poland against the Russians in 1579 at Polotsk. Thereafter the use of heated projectiles became increasingly important over the next 200 years, especially against ships. During the Revolutionary War in this country, for instance, American and French artillerymen burned the 44-gun British warship Charon with hot shot during the battle of Yorktown in 1781. Perhaps the most famous use of hot shot took place in 1782 during the Second Siege of Gibraltar when French and Spanish forces attempted to use ten large floating batteries in a bombardment against British defenders. The floating batteries had been made of heavy construction and were thought to be invincible. However, British artillery in Gibraltar used hot shot to destroy nine of the ten batteries and inflict a loss of 1500 crewmen.

During all these instances the usual method of heating cannon balls was by covering them in the coals of a large wood fire, or heating them on metal grates placed over a fire pit dug into the earth. A significant improvement over this time-consuming method was soon developed by the French, who employed the use of air furnaces to heat shot in their batteries on the Mediterranean at the mouth of the Rhône River in 1794. Little wonder that when master French engineer General Simon Bernard came to the United States in 1816 to head the Board of Fortifications for the construction of permanent forts to defend the U.S. coast, the idea of Hot Shot Furnaces based on the French pattern came with him. The chain of U. S. seacoast forts built between 1817 and the Civil War, of which Fort Macon was a part, thus had one or more Hot Shot Furnaces built as part of their standard defenses.


Hot Shot Furnaces are brick structures varying in size as to the number of shot they are to hold and the number of guns they are to serve. They are about six to eight feet wide, and from eight to over 30 feet in length. A brick chimney is situated at one end with a firebox located in the front or side of the opposite end. The interior of the furnace is lined with fire brick and contains a set of sloping iron rails to hold rows of cannonballs. Rows of iron rods pass through the furnace from one side to the other and are fitted on each end with bolts and “star” braces to support the weight of the shot rails and roof. Cold cannonballs are placed in the furnace and allowed to roll down the inclined rails in rows. The first halls are directly over the firebox at the low end and are heated “cherry red.” As they are removed, the next balls roll down into their place and are likewise heated. A large furnace might hold 60 or more cannonballs.

Three men are required to manage a furnace. One maintains the fire and adds cold cannonballs. A second man removes heated cannonballs from the furnace and the third man cleans them. As might be imagined, special tools are required to handle hot shot. An iron fork is used to remove the heated shot from the furnace. The shot is placed on a stand and cleaned by rubbing off any loose surface scales with a rasp. A pair of tongs with circular jaws are used to pick up and handle the shot at the furnace. To carry the shot up to the cannons, hot shot ladles are used. The ladle has an iron cup for the cannonball which is fitted with one or three handles. Cannonballs under 24-pounder size are carried by one man with the single-handle ladle. Cannonballs of 24-pounder size and up require the three-handle ladle, carried between two men like a stretcher.


The process of loading hot shot into a cannon is a ticklish operation, as one might imagine. Care is taken in order that the red hot cannonball does not somehow ignite the cannon’s powder charge prematurely and thereby kill the cannoneers who are trying to load it. The powder charge, contained in a cartridge bag, is always loaded first, as normal. The cartridge bag is usually double- bagged when using hot shot to ensure that no powder grains are able to leak out into the cannon’s bore as it is rammed down the cannon. Once the cartridge bag is in place in the bore, something obviously has to be placed between the bag and the red hot cannonball to prevent an unwanted explosion. For this purpose wads of moistened clay or more commonly, wet hay are used. The wad is rammed down the cannon bore against the cartridge bag, shielding it from the red hot cannonball which follows. The cannonball is next and is unable to burn through the wet wadding to reach the cartridge bag. If the cannon is to be fired at a downward angle, yet another wet wad is rammed down against the ball to secure it against rolling forward. Thus the cannon has been loaded in complete safety.

A couple of questions might come to mind at this point. First, does the red hot ball eventually burn through the wadding if the cannon is not fired? No. There is little oxygen available way down in the cannon’s bore to aid combustion and the ball does not burn through. In fact it can completely cool down to normal without ever igniting the cartridge bag. However, the ordnance manuals of the period do specify firing the hot shot with little delay because considerable steam is produced which would eventually dampen and ruin the gunpowder charge. Second, does the cool air tend to reduce the temperature of the cannonball as it flies through the air to the target after it is fired? No. In fact the air friction caused by the cannonball speeding through the air adds to the temperature. The cannonball can even be made to ricochet upon the surface of the water several times without losing enough heat to ignite wood.

Another trick of the trade with hot shot is to fire it with a reduced powder charge, usually amounting to 1/4 to 1/6 of the weight of the cannonball. With a full service charge of powder the ball would burst completely through the hull planking of a ship or penetrate so deep into the planking as to be deprived of air as the wood fibers closed up around the hole. The reduced powder charge allows the ball to lodge only within the first 10 or 12 inches of the hull planking where it can still get sufficient air for combustion. Another advantage of the reduced charge is that a lower velocity is produced on the ball which causes a greater splitting and splintering of the wood for burning.


The original engineering specifications for Fort Macon called for three Hot Shot Furnaces to be built. However, when the fort was completed in 1834, none of the three had been built, nor were there even any cannons sent to arm the fort until the following year. On January 17, 1836, Engineer Lieutenant Alexander J. Swift was authorized to build one Hot Shot Furnace at the fort. The furnace was commenced later that month and probably was not completed until March, 1836, due to delays in obtaining lime, cement, fire brick and metal work from New York. Its location is in the parade ground beside the Southeast Stairs where easy access is available to the guns above bearing on the sea.

At the end of 1840, Engineer Captain Robert E. Lee inspected Fort Macon and decided a second Hot Shot Furnace was needed to serve the seaward guns on the outer wall, or Coverway. He estimated its cost would be $300. Accordingly, the addition of a second furnace was one of many changes made to the fort by the Engineers during 1841-46. Unfortunately, little is known about this second furnace. It probably was similar in size to the first furnace and was built in the ditch probably close to the south angle of the fort where stairs gave access to the guns above. The furnace was scheduled for construction during October, 1843, but no mention has been found exactly when it was built.

Today the foundation of the old 1836 furnace is still visible on the parade ground as the only tangible reminder of their existence. The foundation is a brick rectangle measuring about 6 1/2 by 10 1/2 feet. The outline of the firebox/ash pit can still be made out at the front end of the foundation. Currently, it is planned to rebuild a replica furnace on this original site. Although no plans for either of the fort’s original furnaces exist, plans of furnaces at other forts can still be obtained from the National Archives. Original furnaces even still exist at Forts Jefferson, Massachusetts, Pike, Morgan, Knox, Niagara, and the Castillo de San Marcos for comparison.

In rebuilding the 1836 Hot Shot Furnace, the Friends of Fort Macon have the opportunity to do something unique and remarkable. They will be building a structure which has not been built in this country by anyone since the Civil War and they will be replacing one of the most unusual weapons which Fort Macon, or any fort, typically had in its arsenal of defense.