The catch is the word "sturdily." The part of the ship structure to which the gun is attached must be sturdy enough so as to withstand the force and transmit it to the rest of the ship. It would not be very good for continued employment as a ship designer if the bulwark broke off.
While this is less likely to be an issue for an ironclad, in which the gun is connected to the armor, it's a concern with wooden ships. Still, wooden bomb ketches were constructed in such a manner as to absorb the shock of firing a heavy mortar. And "non-recoil carronades were first used by the Arrow in 1796. . " (Blake 140).
The recoilless guns of land warfare use a different cheat; they eject a counterblast of equal momentum (mass * velocity) in the opposite direction at the time of firing. This may be propellant gas, or liquid or solid material that is forced out by the gas. The problem, of course, is that it is dangerous to stand behind the breech end of the cannon in the path of the counterblast. (Not that standing behind a recoiling cannon was smart.) The German Bohler 78 mm had the counterblast fired obliquely upward, to reduce the risk to crew (Hogg 135); but this would also require a larger blast to compensate for the angle, and create a downward force on the deck. Also, these recoilless systems are very wasteful (~80 %) of propellant.
An intermediate solution is a muzzle brake. This is a baffle attached to the muzzle end; the gases escaping with the projectile are deflected sideways and upward, so that they don't create a backward reaction force on the gun carriage. (Payne 265).
Gun Laying
A gun is elevated vertically, and traversed horizontally, so that with the chosen projectile and charge, and discharged at the correct moment, it will strike the target. The greater the range, the more important it was that the gun be elevated to compensate for the fall of the projectile, and traversed to lead the target.
Elevation (the angle between gun bore and horizontal, not the height of the gun above sea level) was relatively straightforward. Since about 1450, cannon were cast with trunnions-short lugs extending on either side of the barrel to serve as an axle. This fitted onto the gun carriage, and the barrel pivoted up-and-down around it.
Maximum elevation was dependent on the geometry of the barrel and carriage, but probably was about 15°-the highest value typically given in nineteenth-century gunnery tables. One source says the limit was about 7°, but that ships could hit a more elevated target by firing on the up-roll. (Volo 256). Douglas (252) proposed that nineteenth-century ships be equipped with "dismantling guns" that could achieve at least 30° elevation.
In the 1630s, changing barrel elevation was a little tricky. There was a wedge (quoin) under the breech end. The barrel would be lifted off the quoin with handspikes, and then the quoin would be moved forward or backward to adjust the elevation angle. That was enough for varying the degree of positive (above horizontal) elevation, but depressing the barrel below the horizontal was trickier. A wad had to be rammed down the muzzle so the ball wouldn't roll out, and it might be necessary to insert an additional or thicker quoin under the breech so the barrel would point downward. It should be noted that when the gun recoils, the position of the quoin may be disturbed.
You might logically wonder whether this cumbersome quoin system was adopted because no one had thought of equipping the gun with an elevating screw. The elevating screw per se had already been invented, as is evident from drawings by both Leonardo da Vinci and Albrecht Durer. (Kinard 70). However, it was not used in the field artillery of the Thirty Years' War (Guthrie 15), let alone in the technology-lagging naval artillery. Deane (48) says that a Jesuit, in 1650, was the first to equip a land gun with an elevating screw. As for naval guns, the British introduced elevating screws around 1790, for use on carronades. (Lavery 132).
A screw provides mechanical advantage-it is the equivalent of an inclined plane that has been coiled up. The pitch of the screw determines how much the gun is elevated per turn; the smaller the pitch, the slower the elevation, but the finer the control. Modern tests on nineteenth-century 6-pounders revealed that each turn elevated the piece by 30–60 arc-minutes, and that the obtainable accuracy of elevation was about 2 arc-minutes. (Hughes 19).
Without the elevating screw, it took at least four men to change elevation: at least two with handspikes to lift the breech end, the "first Captain" to sight the gun and judge when it was at the right elevation ("Raise!" "Lower!" "Well!"), and the "second Captain" to adjust the quoins to hold the gun ("Down!) at that elevation. With the screw, one man could sight the gun while turning the screw to suit.
Nonetheless, to make a rapid, albeit crude, change in elevation, quoins were apparently faster, which is why carronades were also given molding under their breeches. (Lavery 132). Quoins were also needed if the elevation change was greater than that permitted by the screw (Douglas 163).
In the case of field guns, "the heavier pieces like the 18-and 24-pounders were still elevated by quoins as late as the early 1800s." (Manuoy 55). Quoins were also still used with siege guns. I suspect that this was because there were technological limitations at the time on the pitch or the compressive strength of the screw, and therefore on how heavy a weight could be lifted. The logical solution was to increase the mechanical advantage by using gears. And from there, the next step was to provide power assistance, e.g., from an auxiliary steam engine or an electric motor, rather than relying on manual operation.
In canon, elevation screws are apparently in use by the Danes in 1634. Offord, "The Bloody Baroness of Bornholm" (Grantville Gazette 18).
Traversal. For a target which is not moving relative to your gun, you traverse the gun so it points horizontally at the target. If the target is moving, you must "lead it" — point to the place it will be when the projectile arrives.
The wheels of the standard naval carriage all rolled forward and backward, and therefore would not have made it any easier to turn the barrel toward the bow or stern. The carriage had to be turned to or fro by brute force.
I own a storage cart with four swivel casters, i.e., wheels with a pivotable connection to the cart. A cannon, of course, is a lot heavier than a storage cart, but internet searching reveals that some caster manufacturers (e.g., Hamilton) claim that their casters can support up to ten tons. Of course, I have no idea whether we have the metallurgical skills to duplicate these casters at a reasonable cost, but it shows that the idea of putting such on a cannon carriage isn't absurd. But perhaps it would make the cannon too easy to move sideways, causing them to shift as the ship pitched.
A pivot mount, of course, would make traversing much easier, and could be equipped with a traversing screw or gear. With a simple slide mount, traversing the gun would be impossible. However, for carronades, the slide bed itself was mounted on a pivot, and on the inboard end there were two small wheels, whose positions established the radius of the traverse. Since the recoil motion was on the slide, and didn't affect these wheels, they could be positioned to roll circumferentially, making the traversal much more efficient. (Blake 140).
There were basically two ways of mounting a turret; it could rotate around a central shaft (Ericsson's USS Monitor) or on a circular track with ball bearings (Eads' USS Winnebago) (cityofart.net).
There were aircraft and tank turrets that were manually rotated, but naval turrets were larger and heavier. While the earliest naval turrets were hand-cranked (Kinard 237), the USS Monitor was equipped with a steam "donkey" engine to turn its turret, and that quickly became the mid-nineteenth-century norm. However, steam engines radiate heat, making conditions in the turret unpleasant, and of course there's the risk of scalding the crew if a leak occurs. There was some experimentation in the late-nineteenth century with compressed air systems, but the necessary high working pressures posed dangers of explosion. By the early-twentieth century, turret power was either hydraulic (British) or electric (American) in character. (Fullam 214ff).
Elevation Measurement
It does you no good to calculate and adjust the elevation of the gun if you can't judge wh
ether you have done so correctly.
Pre-Ring of Fire (RoF), elevation was determined using a gunner's quadrant, first described by Tartaglia (1545). This was an L-shaped instrument with a plumb bob and an arc scale. One arm of the L was placed inside and parallel to the bore; the angle at which the plumb bob intersected the scale was read off.
Elevation may also be read off by a clinometer. A viscous liquid might half-fill a disk, and then the level of the liquid (an artificial horizon) is compared to an angular scale inscribed on the face of a disk. This is analogous to the aircraft inclinometer.
Or an object, a bubble or a bead, moves inside a tube filled with a viscous liquid, as in the spirit level used by carpenters, and the tube is graduated to show the angle of inclination.
Unfortunately, the spirit level doesn't provide much of an angle range. So a military clinometer has the spirit level mounted on a pivotable arm, which points to a scale that specifies the "zero" angle for the spirit level. The arm is attached to a frame whose base is placed on a receiver attached to the gun barrel. Since the outside of the gun barrel is not parallel to the bore, this receiver must be adjusted, just like gun sights, or an offset must be dialed in. To set the gun to a desired elevation, you lay the clinometer on the receiver, adjust the arm to point to the desired value on the main scale, and elevate the gun until the level bubble in the level vial is centered.
Some kind of pocket clinometer, most likely of the kind used by geologists, came through the Ring; see Jones, "Schwarza Falls" (Grantville Gazette 5).
Gun Sights
Open Sights. The simplest method of sighting was to sight along the "line-of-metal," the top of the cannon, directly at the target. However, the cannon was wider at the breech end than the muzzle end, so the line-of-metal was depressed 1–3° (Douglas 293; Beauchant 16) below the line-of-fire, depending on the exact geometry of the cannon. This could be corrected for by adding a "dispart," a vertical sight at the muzzle end, with a height equal to half the difference in diameters. If the bore wasn't quite center, this still wouldn't be quite right, but a gunner could customize the dispart for the peculiarities of a particular gun.
The tangent sight was an adjustable rear sight. The sight was on a bar, graduated either in degrees or ranges, and fitting into a socket at the center or on the side of the breech. The name is derived from a trigonometric relationship, the required height of this rear sight is the product of the distance from the rear sight to the front sight, by the tangent of the required angle of elevation. This may seem a simple concept, but it doesn't appear to have been used on artillery until it was introduced by de Gribeauval in the late-eighteenth century. (Cummins 25). Bear in mind that its use implies setting a specific angle of elevation, rather than just sighting on an aiming point. (Ruffell).
In canon, the guns of Simpson's 1634 navy have ring-and-post sights. (1634: The Baltic War, (TBW) Chap. 38).This combines a front (post) and a rear (ring) sight.It can be advantageous for the "ring" part to have several concentric circles; these can be useful in "stadiametric ranging" (measuring the angular width of a target of known actual width). A V-or U-notch is a possible substitute for the ring.
You have to hold your head just right to keep the ring and post aligned. It's also hard to use if the target is far away; bear in mind you are trying to keep in focus the target, the rear sight and the front sight, all at different distances.
Telescopic Sights. In Cooper, "Seeing the Heavens," Grantville Gazette 16, I described the state of the telescopic art as of the RoF. In 1640-41, William Gascoigne mounted telescopic sights-essentially, a Keplerian telescope with crosshairs in the focal plane-on various scientific instruments, including a micrometer and a sextant. However, the first documented use of a telescopic sight on a firearm was in 1835, and that was for use with a percussion ignition sporting rifle. (Pegler 50). And as far as I know, the first use of a telescopic sight with artillery was in 1857. (Strauss 587).
If this long time lag from the invention of the telescope to its use in gunnery surprises you, consider this: it doesn't matter if you can see the pimple on the enemy helmsman's nose if your powder and shot are so inconsistent in character, and ship motion so erratic, so you can't even hit the enemy ship with more than one shot in ten.
In canon, the best of Krak's Shooters have been given up-time telescopic sights for their flintlock rifles. (Flint, 1633, Chapter 35).
Since telescopes provide a magnified image, they necessarily have a narrowed field of view, and the eye needs to be close to the eyepiece to get that view.If the telescope is attached to a cannon, you must move your head away quickly when you fire, lest recoil result in an unpleasant experience.
Reflector Sights. A half-silvered diagonal or curved mirror can be used to overlay a virtual image of an illuminated crosshair, harmonized with the gun bore, over the field of view. While optical tricks using partially reflective mirrors are much older, the reflector gunsight reportedly was invented in 1900. A reflector sight is easier to align with the target than is an open sight. But please note that open sights were still used four decades later.
In shooting at a distant target, you need to allow for the "drop" (from gravity) and the "lead" (to anticipate relative target motion). So you have to offset the line of aim from the line of bore so that the projectile would hit the target.
Initially, gunners had to offset manually. However, analog computers were developed to calculate this offset and manipulate the optics accordingly. On these "computing gun sights," the gunner had to estimate the size of the enemy and fit the image within a reticle so the range could be calculated stadiametrically. Anti-aircraft guns had fancier "predictors."
Gyro Sights. The gyro sight was developed during WWII for aircraft (and anti-aircraft) use. The reflector was linked to a spinning gyro and this made it possible for the sight to compensate for the aircraft's own motion by adjusting the reflector. (Jarrett 190).
Firing Mechanism
The period gun has a vent (touch hole) that connects the powder chamber to the outside world. In preparing to fire the gun, the touch hole was filled with a "priming" powder, and some powder was deposited on the barrel just behind the touch hole. A linstock (forked staff) was used to bring a lit "slow match" (a slow-burning fuse, made by impregnating a rope with a saltpeter solution) over to the surface powder, igniting it. It, in turn, ignited the powder in the touch hole proper, which ignited the powder in the chamber. (Little 145).
Unfortunately, this process tended to erode the vent. Consequently, come 1697, gunners inserted disposable metal (tin) tubes into the vent. The tubes were filled with a paste of powder, gum and water, and loose powder was sprinkled on top. In 1778 the British Navy replaced the metal tubes with goose quills. (Rufell).
After 1700, it became customary to use the slow-match just to light a "portfire," a paper tube, closed at one end, filled with a mixture of gunpowder, sulfur and saltpeter in a linseed oil base; it burned rather like a motorist's emergency flare. (Peterson 66).
I imagine that we will leapfrog portfires and proceed to mechanical ignition. The first such was the Douglas flint lock (1778), which was actuated by a lanyard that pulled its trigger. In 1842 it was replaced by the Hiddens percussion lock; a hammer struck a percussion cap. (EB11/Ordnance).For the reasons why the 1633 NUS army was armed with flintlocks, not percussion locks, see Grantville Firearm Roundtable, "Flint's Lock" (Grantville Gazette 3).
The "firing interval" is the time elapsed from when the gun captain activated the ignition mechanism to when the primer actually ignited. (There would of course be a further delay until the projectile actually left the gun barrel). With the percussion lock, the firing interval averaged 0.13 seconds. (Meigs 195).
The percussion cap contains a primer, a fairly sensitive explosive mixture that in turn sets off the explosive. The first primer developed was mercury fulminate (1807). According to canon, certain reckless souls are making it. See Offord, "Dr. Phil Zinkens A Bundle" (Grantville Gazette 7); Offord and Boatright,
"The Dr. Gribbleflotz Chronicles, Part 2: Dr. Phil's Amazing Essence Of Fire Tablets" (Id.); Mackey, "The Essen Steel Chronicles, Part 2: Louis de Geer" (Grantville Gazette 8); Evans, "Thunder in the Mountains" (12); Zeek, "One Fine Day" (20); Offord, "A Change of Hart" (25); Howard, "The Baptist Basement Bar and Grill" (32).
While these stories emphasize the dangers of manufacturing mercury fulminate, there are other problems. Specifically, it was found (in 1897) that the mercury in the primer became amalgamated with the brass of nineteenth-century cartridge cases, embrittling them. These cases were a large part of the cost of a cartridge and the "brass" (couldn't resist) wanted to be able to reuse them.
Accordingly, mercury fulminate was replaced with potassium chlorate (historically, first synthesized in 1786). That, too, has appeared in canon, in the percussion caps for the French "Cardinal" rifles. (TBW Chap. 27, 45).
It's not a panacea. When a gun using a potassium chlorate primer is fired, the priming reaction generates potassium chloride, which is deposited on the bore. This salt greedily absorbs water, causing rusting. In OTL, it wasn't until 1922 that potassium chlorate was identified as the cause of the rust, but Grantville's gun buffs may already know about the problem.
A non-corrosive primer, based on lead styphnate, was patented in 1928. It's likely that gun owners in Grantville have heard of it. Condensed Chemical Dictionary reveals that this is the legal label name for lead trinitrosorcinate (311), that the latter is made from magnesium styphnate and a lead salt, the former in turn being made from magnesium oxide and styphnic acid (312), and that styphnic acid is made by nitration of resorcinol (830; cp. 759).
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