Heated shot

It was rendered obsolete in the mid-19th century when vessels armored with iron replaced wooden warships in the world's navies.

Also at around the same time, the replacement of solid-iron shot with exploding shells gave artillery a far more destructive projectile that could be fired immediately without preparation.

[2] The French Romaine-class frigates originally also featured the device, but they proved impractical, dangerous to the ships themselves, and were later discarded.

These time-consuming methods were improved by the French, who used specially-constructed furnaces to heat shot in their artillery batteries at the mouth of the Rhône River in 1794, although artillery units would continue to use a grate constructed of iron bars and earth when a purpose-built shot furnace was unavailable.

[1] The United States incorporated hot-shot furnaces into the design of coastal fortifications during the construction of the Second System of seacoast defenses, just prior to the War of 1812.

A hot-shot furnace was typically a free-standing brick or stone structure with special iron racks and grates, varying in size according to the number of round shot they were to heat and the number of cannon they served – a large furnace might hold 60 or more round shot.

The interior of the furnace was lined with fire brick and had sloping iron rails sized to hold round shot.

Cold round shot were placed in the furnace and allowed to roll down the inclined rails in rows.

If proper loading precautions were taken, the wet wad could protect the gunpowder cartridge from premature ignition even until the heated shot had cooled down.

However it was better to fire the gun quickly as water boiled from the wet wad could condense in the gunpowder charge if there was an excessive delay.

[15] Also, if a shot embedded itself too deeply into the target, insufficient air would reach it to effectively start a fire before it cooled down.

From the time of lighting, around an hour was required to bring seven hundredweight (320 kg) of pig iron to its melting point of 1,150 to 1,200 °C (2,100 to 2,190 °F) – this amount could fill 30 8-inch shells.