April 10, 2019

Shells Part 1

When I discussed battleship main guns, I mostly glossed over the shells that they fired. The time has come to rectify that omission, and discuss the wide variety of shell types that have seen naval service over the centuries.

Early shells, with shot on the left1

In the age of sail, the basic naval projectile was round shot, a simple round chunk of metal. This had the advantage of being cheap and fairly effective at making holes in a target. The problem was that poking small holes in something as big and tough as a ship, even a wooden one, was not a particularly fast way to kill it. A few men might be killed by flying splinters, but the holes were easily plugged by the ship's carpenter, and it took an awful lot of battering to actually kill another ship. Ordnance designers thus came up with a number of specialized projectiles that would have other effects. Chain shot, when two halves of a cannonball were linked by a chain, was used to slash through rigging and batter masts. To attack the enemy crew, canister or grapeshot was used, turning cannons into giant shotguns. However, all of these specialized projectiles lost velocity quickly and were thus limited to short range. The only way to improve round shot as a ship-killer was to heat it in a furnace so it would set fire to the target. However, this had serious drawbacks. The shot had to be heated, which took time, and the safety implications of trying to use heated shot from a wooden ship are obvious. As a result, its use was mostly confined to coast-defense batteries, although a furnace for heating shot was installed aboard USS Constitution.2

Canister, grape and shrapnel

The most obvious way to get shot to do more damage was to hollow it out and fill the inside with explosives, which would then be ignited by a fuze of some sort. Early attempts to use these "shells" were thwarted by fuze problems, and until the early 1800s, their use was limited to specialized high-angle low-velocity weapons like howitzers and mortars.3 Higher-velocity guns, which were necessary to fire the projectiles at low angles, often damaged the fuzes, causing duds or setting the shells off early. It was not until the 1820s when a successful shell-firing gun suitable for shipboard use was designed, by French general Henri-Joseph Paixhans. The so-called Paixhans gun fired a spherical shell, with the fuse pointing forward as the gun was loaded, where it would be ignited by hot gasses slipping around the shell, but not destroyed. The fuse was cut somewhat longer than the expected time of flight of the shell, with the hope that it would lodge in the target and then explode.

The Russians destroy the Turkish fleet at Sinop

The French, American and Russian navies adopted the Paixhans gun in the 1840s, and they saw sporadic action until 1853, when the Russian use of shells against the Ottoman fleet at the Battle of Sinop brought them into the public eye. A Russian squadron annihilated a group of anchored Ottoman frigates in about half an hour, killing almost 3,000 Turkish sailors at a cost of only 37 men. This battle, one of the opening moves of the Crimean War, was a major driver in the development of the ironclad.

A Paixhans Gun

One drawback of the Paixhans gun was that it threw its projectiles at fairly low velocity, reducing range and accuracy and making it ineffective when firing shot. In the 1850s, the Dahlgren gun, developed by American naval officer John Dahlgren, was created to solve this problem. It was considerably thicker than the Paixhans gun, allowing it to throw its projectiles much faster. It could handle both shot and shell, and the distinctive bottle shape was a common sight on land and sea throughout the American Civil War.

John Dahlgren with one of his guns

When ironclads arrived on the scene, shot gained a new lease on life. Shells would either bounce off armored vessels or smash to pieces, and only solid chunks of metal stood any chance of piercing their plate. But unarmored warships soldiered on in many roles, and so the shell never died completely. This era saw great improvements in naval ordnance, notably the widespread introduction of rifling and the growth of guns. Rifling meant that shot and shells flew in a predictable orientation, and spheres were swiftly replaced with longer, pointed projectiles, which gave greater range and punch. This allowed another improvement in shell design.

Palliser Shot, Common Shell, and Shrapnel for a 12" 35-ton RML gun

The idea of a shell that detonated on impact had long been attractive, as existing shells might bounce off or even have their fuses extinguished. It was also incredibly difficult to implement. The problem was that the shell's orientation on striking the target couldn't be controlled, and it was hard to build a mechanism that could set it off reliably and that didn't lead to lots of shells bursting in or very near the gun that fired them, which tended to make gun crews irritated. The new rifled guns fired shells that would always hit nose-on, greatly simplifying design and allowing shells to go off on impact.4 This made them much more useful, as they didn't have to worry about bouncing off or splitting open before detonating. However, shells were still only effective against the outside of armored targets. The fuzes didn't have the delay necessary to let the shell get through the armor, and the filling, which was still black powder, was often sensitive enough to go off on its own before it made it through the plate. The standard explosive-filled shell, usually made of cast iron, became known as the Common Shell, a moniker it would bear for the next century or more.5

6" Palliser shot

Shot also saw development during this period, most notably the development of a chilled cast-iron shot by Major William Palliser. The so-called Palliser shot was cast into a special mold where the head was chilled to make it harder while the body was cooled more slowly to give toughness, giving good performance against wrought-iron armor. Some versions, known as Palliser shells, were filled with powder, which was simply set off by the impact, although effectiveness was still limited because it detonated outside of the armor.6 However, improvements in armor soon began to render Palliser shot obsolete. It stayed in inventory for several decades because it was very cheap compared to later armor-piercing projectiles.7

A slightly later set of shells for the 12" 35-ton gun

All of this takes us only through the start of the breech-loading era (at least in British service), but that era would see more great strides made in naval projectiles. I'll pick up the story there next time.

1 This photo and the one below it are from my collection, taken at the fantastic Field Artillery Museum at Fort Sill.

2 An interesting variation on heated shot is the molten iron shell, which was a shell, lined with horsehair and loam, that was filled with molten iron from a specialized furnace. On impact, the shell would shatter, releasing the iron to start fires. Because of the insulation, the shells were easier to handle, and somewhat safer, although they were soon rendered obsolete by improved explosive shells and the decline of the wooden ship.

3 Mortars were taken to sea in bomb vessels, but these were specialized vessels for attacking coastal positions, and rarely if ever engaged other ships that weren't anchored.

4 I plan to go into the development of fuzes at some point, so I'll save the details on these for later.

5 "Common" was probably meant to contrast with the other type of shell at the time, shrapnel. This was essentially a canister full of metal balls, with a bursting charge that would scatter them. If the time fuze was set right, this would be right over the enemy. I'm not going to go into more detail, as shrapnel was rarely used at sea, even though it was provided for many naval guns, which were also used on land.

6 For context, this filling looks to have been 1-1.5% of the shell weight, while a common shell of the era was around 6% explosives by weight.

7 I can't really tie this into the narrative, but I feel compelled to link to the Wiki article on gas checks for British RML heavy guns that I discovered while working on this. It's really, really good, and done by someone I think I'd like to meet.


  1. April 12, 2019AlphaGamma said...

    On bomb vessels: They had to be exceptionally strongly built to cope with the recoil from the mortars, which meant that after they became outmoded militarily, many were repurposed as polar exploration vessels. The Antarctic volcanoes Mount Erebus and Mount Terror are named after James Ross's expedition ships, both of which were former bomb vessels, and were later lost with Franklin's expedition to find the Northwest Passage.

    Terror's sister ships were Vesuvius and Beelzebub, while Erebus was part of a class that included Thunder, Infernal and Meteor- I think the Royal Navy had more fun than usual picking names for bomb vessels. And yes, this does mean that there is a volcano named after a ship which has a sister ship named after a volcano...

    On destruction of ships by cannon fire: In the round-shot era, this was rare. Exactly one ship was destroyed at the Battle of Trafalgar, the French Achille. I believe what happened there is that a fire broke out in the rigging (possibly something to do with a match kept up there to light grenade fuses, as sailors in the fighting-tops would throw grenades from them during battle), and when the burning mast was brought down by gunfire, the rest of the ship caught fire then exploded.

    Plenty of others were "mission killed" either by casaulties to the crew or by damage to the masts and rigging, and many of those were either burned by their captors or lost in the storm after the battle.

  2. April 12, 2019bean said...

    I think the Royal Navy had more fun than usual picking names for bomb vessels.

    This is reasonably common when people are asked to name minor ships that fall outside the traditional naming structure and class conventions.

    And I will cheerfully admit to not making a full examination of the weapons of the age of sail, mostly because that wasn't really where I was trying to go with this post.

  3. April 12, 2019AlphaGamma said...

    Don't worry, I'm happy to keep adding Age of Sail asides in the comments if you don't mind, or to stop if you do.

    In terms of heated shot, I was wondering about the practicality of its use at sea. It turns out the answer was "not very". The red-hot 24-lb cannonballs could only be carried from the furnace to the guns one at a time, and the Constitution carried only one pair of tongs and ladle for doing so. There was no question of firing a red-hot broadside, as the first shot would have cooled by the time the last one was loaded.

    With this and various precautions that had to be taken to stop the heated shot igniting the charge in the gun, I think the only intended use for the shot furnace would have been in a chase, where many fewer guns would have been in use anyway.

    One more peaceable use for red-hot shot was found by the Danish War Ministry, which used them for heating in the 19th century. From what I've heard, they installed a shot furnace in the basement, from where somebody would take a cart full of red-hot cannonballs and deposit them in the various office fireplaces...

  4. April 12, 2019bean said...

    Go right ahead. I have nothing against the Age of Sail, I just don't care as much about it as I do about the steam and steel era. If you want to talk about it at greater length, I have Friday slots you're welcome to.

    That's a good thought on the heated shot furnace on Constitution, and it was swiftly confirmed when I went hunting for information on it. The original intent was to use it from the stern guns if the ship was outmatched, not for general service.

    And I definitely didn't know about the Danes using them that way.

  5. April 15, 2019AlphaGamma said...

    Thanks very much for the offer of the Friday slots- I don't think I currently have time to take you up on it, but I'm honoured that you made it.

  6. April 15, 2019bean said...

    Fair enough. It's something I'd like to cover/have covered eventually, but I'm pretty sure I'll be able to think up new topics at a rate great enough to keep me in the post-1850 era indefinitely.

  7. November 08, 2020brian miller said...

    The fuse for the orriginal shrapnel spherical case shot was the simple wood stemed "carrot" and was believed to premature almost 20%. This was considered acceptable as the tiny opening charge caused insignificant damage to the barrel while the 80% that burst in front of the target,if the fuse was cut correctly,caused havock at a range no case shot could reach.Was paixhans fuse not wood bodied? Splits in the wood body or the fuse not being driven into the shell body hard enough, adecade later were eliminated by the boxer metal fuse but we dont see this till the 1850s a decade later. THE Paixhans system used some sort of obturation system that protected the fuse during its long passage up the high pressure barrel. Has anyone a clue

Comments from SlateStarCodex:

Leave a comment

All comments are reviewed before being displayed.

Name (required):

E-mail (required, will not be published):


You can use Markdown in comments!

Enter value: Captcha