The Hot Shot Oven

Castillo de San Marcos

Castillo de San Marcos. Photo by the author via Flickr

The oven is that small structure with the chimney you see in the distance. I always wondered why it was located outside the fort’s walls. The article below explains that. Note the semi-circular structures in the grass to the left side of the photo. Those were gun emplacements also built by the U.S. Army after Florida became part of the United States.

The following article was compiled by workers of the Writers’ Program of the Work Projects Administration in the State of Florida in 1940. You’ll find a copy of the actual manuscript at Florida Memory.

The substantial little furnace for heating cannon balls on the seaward side of Fort Marion (Castillo De San Marcus) has been an object of interest since its erection in 1843. These auxiliaries of the artillery have been common to forts erected on the seacoast since revolutionary times, and the shot heated in these ovens were very effective against wooden ships.

The hot shot furnaces were all about the same size and held 60 or more shot, according to the caliber. The shot being placed in the furnace cold, it required one hour and fifteen minutes to heat them to a red heat, but once the furnace was hot, a 24-pounder shot could be brought to red heat in 25 minutes; the 32 and 42-pounders requiring a few minutes longer. An unusual circumstance concerning the heating was that the balls expanded under the heat but did not
return to their normal size after cooling.

Inside the shot oven.

A look into the shot oven at the Castillo. From the author’s collection at Flickr.

Once the balls were cherry-red or white hot, they were taken from the furnace with iron forks, scraped carefully with rasp to remove scale, and carried in ladles to the cannon. The ladles were formed of an iron ring, the interior of which was beveled to fit the ball, with two wooden-handled arms inserted.

Several other implements were attached to the furnace also; pokers for stirring the fire, rasps, tongs with circular jaws for taking up shot, iron rake to remove cinders from ash pit, tub for cooling implements, rammer with head covered by a circular plate of sheet iron of larger diameter than the ball to remove clay from bore when clay wads are used, and a bucket. Many of the implements were furnished in twos so that one set could be cooling in the tub while the others were in use. When the battery was in action it took three men to serve the furnace, and handle the tools.

In siege batteries, or in other situations where there were no furnaces available, a grate was used for heating shot. In a painting of the Battle of Niagara, during the War of 1812, an American woman is shown heating shot on a grating of this sort, while another rushes the cherry-red balls to waiting gunners. In loading the projectile, gunners elevated the cannon’s muzzle sufficiently to allow the ball to roll in, and rammed the cartridge or powder bag home. After the powder was seated, a dry hay wad was rammed against it, then a wet hay or clay wad. Next the powder bag was pricked open and primed through the vent, and a wet sponge passed through the gun. Finally, the hot shot was rolled in packed with another wet hay or clay wad, the match was applied to the touch- hole, and the meteoric projectile bounded across the billow.

The cartridges (powder charge minus shot) for hot shot were little different than those used for ordinary projectiles, being made of cannon cartridge-paper, or parchment well pasted to prevent the powder from sifting out.  Sometimes two bags were used, one within the other. When clay wads were used they were cylindrical in form, about one caliber long, and were well moistened.  Wet hay wads were preferable, however, and these were soaked in water for about 15 minutes then allowed to drip.

When the wet hay was used, steam was often seen to issue from the touch- hole or vent as soon as the ball was rammed home, but as this was the effect of the heat of the ball against the water contained in the wad no danger resulted from it. It is said that the ball could cool in the gun without the charge taking fire, but shots were usually fired as quickly as possible to prevent the steam dampening and injuring the powder.

It has been argued by some that the cannon ball would cool in its passage through the air towards its objective, but the contrary is true; the temperature of the ball was increased by friction with the air. According to the Ordnance Manual of 1861, a red-hot shot retained sufficient heat to set fire to wood after having struck the water several times!

The penetrations of cold and hot shot into wood were equal under the same circumstances. Charges for hot shot were reduced, however, to one quarter or one-sixth the weight of the shot in order that the ball might remain in the wood and not penetrate too deeply as it was found that the fire was communicated more rapidly and certainly to the wood when the ball did not penetrate more than 10 or 12 inches. At a greater depth the shot would be less effective, as the  communication with the external air was not sufficient for combustion.

With the invention of the ironclad Merrimac and Monitor during the later days of the War between the States the days of wooden battleships were over, and the hot shot furnace became obsolete also. During its heyday, however, the arrival of some of the furnace’s cookery rolling along pitch-oozing decks littered with fragments of power bags, very likely terrified the seamen. Often the ship would go up in flames from ignited rigging, or blow up from a shot to the magazine. Somewhat slower, but just as effective, were shots placed “‘twixt wind and water’,” which smouldered [sic] away in the oaken sides until quenching the blaze was impossible.

Although cold and useless today, the hot shot furnace at Fort Marion still stands on a humble monument to the ingenuity of artillerists who have established the Coast Artillery branch of the Army.


Silent Sentinel

Castillo bayfront sketch

The Castillo de San Marcos has protected the residents of St. Augustine for more than 300 years. Built using a local shell rock called coquina, this fortress was never captured in battle. Instead of shattering its walls, cannon balls either bounced off or were absorbed into them like in a sponge.

Today it is one of our national treasures maintained by the National Park Service and open to visitors daily. To learn more, visit the Castillo’s site at

Dungeon Tales

Bloomfield’s Illustrated Historical Guide was a tourist guide book for St. Augustine in the late 19th century. Max Bloomfield, who identifies himself as the editor, publisher and proprietor, had a shop where he sold newspapers, books and stationery.

Below is his account of the infamous dungeon at the Castillo de San Marcos – also known as Fort Marion.

Under the northeast bastion we find a dark, gloomy dungeon twenty feet long, six feet wide, and nearly five feet high, where not a ray of light can penetrate. This was once built up, and cut off from all communication with the rest of the fort.

Castillo de San MarcosIn 1836 the terreplein of the northwest bastion fell in, revealing a dark and dismal dungeon. We have heard from the lips of a reliable person, still a resident of St Augustine, and who was present at the time of the above accident to the fort, of the following facts: “I stood upon the edge and looked down into this dungeon, and there saw the complete skeleton of a human being, lying at full length, apparently on its back; the arms were extended from the body and the skeleton fingers were wide open; there appeared to be a gold ring upon one of the fingers. Encircling the wrists were iron bands, attached to which were chains fastened to a hasp in the coquina wall near the entrance to the dungeon.”

The military engineer having charge of the repairs of the fort and sea wall, descended into this dungeon, when his curiosity was excited by the discovery, to the northeast, of a broad stone, differing greatly in dimensions and appearance from those of which the wall was built. He noticed, moreover, that the cement which held this stone in its place differed in composition and appeared to be more recent. On the removal of this stone, the present dark and dismal dungeon was disclosed. On entering with lights there were found at the west end, two iron cages suspended from hasps in the wall. One of the cages had partially fallen down from rust and decay, and human bones lay scattered on the floor. The other remained in its position, holding a pile of human bones. The latter cage and contents may be seen in the Smithsonian Institute at Washington.

This stone was removed by the assistance of Mr John Capo (now deceased), an honest old harbor pilot and mason; we have his statement made personally to us, confirming the finding of the two cages containing the skeletons, as presented in this sketch.

From a lecture delivered at the fort by J. Hume Simons, M.D., and afterward published in the Florida Press, we quote:

“The broken cage, with all the bones, except those which I hold in my hand, were buried in the sand mound to the north of the fort. I recognize these as portions of the tibia and fibula (or leg bones) of a female.”* (* Whitney’s Pathfinder)

The following letter and item we quote from Edwards’s Guide of East Florida:

“The story of the finding of iron cages inclosing human skeletons must lose its horrible interest when the following letter is read. It is an answer to one of mine of inquiry on the subject.”

Smithsonian Letter
The following we quote from Dewhurst’s excellent History of St Augustine, which is undoubtedly the true story of the cages and skeletons.

“At the time the Americans took possession of the fort, they found the last casemate, fronting on the court, on the east side, filled with the coquina floor of the terreplein, which had fallen in, as the timbers supporting it had rotted. Naturally this half filled casemate had become the place of deposit for all rubbish accumulated upon any part of the works. In the course of repairs, the rubbish was cleared out of the casemate, and the entrance into the adjoining cell exposed. Entering this cell, and examining the masonry for anticipated repairs, the engineer in charge, said to be Lieutenant Tuttle, U.S.A., discovered a newness of appearance about a small portion of the masonry of tne north wall. Under his instruction a mason cut out this newer stonework, and found that the small arch under which those who now enter the ‘dungeon’ crawl, had been walled up. . . . . Near the entrance were the remains of a fire, the ashes and bits of pine wood burned off toward the centre of the pile in which they had been consumed. Upon the side of the cell was a rusty staple, with about three links of chain attached thereto. Near the wall on the west side of the cell were a few bones. Finding these very rotten, and crumbling to pieces his touch, the engineer spread his handkerchief upon floor, and brushed very gently the few fragments of into it. These were shown to the surgeon then stationed the post, who said they might be human bones but were badly crumbled and decayed he could not determine definitely. Nothing else was found in the cell.*

(* The finding of any bones is denied by Major W. H. Benham, U.S.A., on the authority of a Mr. Ridgely, Lieutenant Tuttle’s overseer. Major Benham took charge of the work upon the fort in January, 1839.)

“The iron cages which have been described as a part of the fixtures of this terrible dungeon, and which it has been said, contained human bones, appear upon the testimony of old inhabitants, to have been found outside the City Gates entirely empty . . . . The cages are described as having had much the shape of a coffin; and the tradition is that a human being had been placed in each, the solid bands of iron riveted about his body, and after life had been extinguished by the horrible torture of starvation, cages and corpses had been buried in the ‘scrub’ then covering the ground north of the gates.

“Doubtless these cages were used for the punishment of criminals condemned for some heinous crime; but whether they were introduced by the Spanish or English is unknown.”

You have now perused Dewhurst’s and Whitney’s cage stories. The following has been related by an old citizen, who distinctly remembers that when a child, of from eleven to thirteen years old, there was a tree situated just inside and close to the City Gates, from which was suspended an iron cage; ’twas just high enough for a man to kneel or lie in. This cage contained a man, and suspended above him, just beyond his reach, was a glass of water and a piece of bread, to make the pangs of hunger, from which he suffered, more keen. At the expiration of a few days, his tortures had made him a maniac, and his shrieks that pierced the air, were something horrible. The person who related the tale is ninety one years old, which makes this event to have happened about eighty years ago, during Spanish rule in St Augustine.


  • Bloomfield’s Illustrated Historical Guide, Embracing an Account of the Antiquities of St. Augustine, Florida, to Which Is Added a Condensed Guide of the St. John’s, Ocklawaha, Halifax, and Indian Rivers–. St. Augustine, Fla: Max Bloomfield, 1882.[]