British Artillery Use

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Description

Cannon and Gun Use

In a siege setting or moving against a prepared position, the 24-pounder (abbreviated to pdr hereafter) was the preferred “offensive” artillery. Starting in 1758, the British regularly employed 24-pdrs against the French. The heavy brass 24-pdrs would be 9.5 feet in length, compared to 8 feet for a medium brass 24-pdr. Field guns often carry the label of light but may include some medium guns, such as some patterns of the brass 12-pdr and heavy 6-pdrs. Instead of the maximum 1/3 service charge of eight pounds of gunpowder, a heavy 24-pdr had a maximum 1/2 service charge of twelve pounds of gunpowder — conferring a higher muzzle velocity and hitting harder at these higher charges (McConnell 1988, Page 392). Maximum hitting power was a key characteristic of a breaching battery, but lower shot velocities could prove more effective against certain wall materials and wall thicknesses. At least on paper, the 18-pdr was often the preferred "defensive" artillery, as an 18-pdr used less gunpowder than a 24-pdr with little loss of range and the targets for defensive guns were not hardened, being freshly dug trench works and earthen batteries. With the rare exception, 32-pdrs were only used where they could be temporarily off-loaded from a large warship and formed into batteries, such as at Louisbourg (1758) and the Siege of Québec (1759). Besides donating the guns themselves, naval gun crews could be assigned to assist under the direction of the Royal Artillery. In this regard, there was considerable cooperation between the British Army and Navy.

Over time, certain gun calibres would come in and out of favor, especially as it regards the fitting of ships (Laverty 1987, Chapter 18). In the early 18th century, the British Navy was replacing the 18-pdr with heavier calibre guns. As a consequence, port defence in North America relied on iron 24-pdrs and iron 12-pdrs. The iron 18-pdr was relatively uncommon, but would again be a common gun in the last quarter of the 18th century, especially with the introduction of new frigate designs. During the Seven Years' War, the British Army did not field brass 18-pdrs but freely utilized both brass 24- and 12-pdrs. With regard to North America, Pitt would send heavy and light 12-pdrs but omitted sending medium 12-pdrs. The medium brass 12-pdr was used by the British in Europe. This gun had many qualities that made it an excellent field gun for maneuvering armies — range, hitting power, and a manageable weight, a full third less than heavy 12-pdrs. It was part of the artillery train fielded during the capture of Belle-Isle off the coast of Brittany, France (1761). There is some suggestion that there was a “shortage” of these guns. In this sense, the gun may have been too valuable in the European campaigns to be sent to North America, but timing could also be a factor here ― the bulk of Pitt's brass trains arrived in North America in 1757 and 1758, not during the later phases of the war.

In 1755, the fortifications guarding the harbors of New York City contained a handful of brass 18-pdrs and 12-pdrs of older patterns. Seven of these brass cannons were captured at Oswego by Montcalm in 1756 ― one 18-pdr, two heavy 12-pdrs, and four medium 12-pdrs. These port fortifications also supplied iron 18-pdrs to several of the Colonial Campaigns, but these guns were old patterns, neglected, and subject to quick bursting (Louisbourg 1745; Lake George 1755; Fort Beauséjour, Acadia (1755); and Fort William Henry 1757). These iron 18-pdrs were massive, weighing between 5,820 and 5,940 pounds with a length of 11 feet (Pargellis 1936, Page 128; Muller 1768, Page xiii; and McConnell 1998, Page 77). Lavery (1987, Page 100) mentions 11 ft. 18-pdrs in records dating to 1698, but no weight is given. The New Englanders essentially negotiate with New York to send them these 18-pdrs because the iron 24-pdrs in Boston Harbor weighed even more. Regular British Army officers wanted nothing to do with the colonial artillery stores.

Artillery pieces did not scale with the size of the shot. Many competing practical elements determined gun lengths, not simply their weights. Aboard ship, where space was at a premium, room to efficiently service the gun was a key consideration and dictated an upper limit on gun lengths. As such, many of the larger guns were of similar lengths. Barrel lengths of ship guns were selected to limit the concussive damage to the ship's hull resulting from their firing. The longer the barrel, the less damage the hull would experience; yet guns would rarely exceed 10-feet, such guns being too heavy to maneuver. By the 1750s, a barrel length of 9-feet for an 18-pdr and 9.5 feet for 24-pdrs and 32-pdrs would be relatively standard. The typical "ship" 12-pdr mounted to a garrison carriage would often be 8.5 feet in length, only a foot shorter than the 32-pdr, but would weigh just 60% of the larger gun. Stripped of its carriage, the barrel of a 32-pdr would weigh between 6,000 and 7,000 pounds. Smaller calibre guns had fewer limitations mandated by weight, thereby allowing for more variation in gun lengths. With smaller calibre cannon, the largest ships would often favor the longest barrels available both for the increase in accuracy and range.

As it regards fortifications, longer barrels had another practical advantage over shorter guns of the same calibre. As the sole of the gun embrasure was sloped downward, guns with longer barrels would extend deeper into the embrasure, and when fired, the longer guns did less concussive damage to the embrasure itself than shorter barrel guns of the same calibre. Similarly, the recommended embrasure width for the much shorter howitzers was wider than for other pieces.

Ricochet fire was intentional and a definite tactic, not just a mere consequence. Against formed troops, solid shot was intended to strike at very shallow angles, literally bouncing several times through the formation. Naval guns commonly used ricochet shot against an enemy's hull ― not unlike skipping a stone on a pond. The ricochet distances could be substantial. For a 12-pdr on hard ground, the shot might travel 500 yards before the initial impact, 250 yards more on the first ricochet, and then 125 yards more on the second ricochet. Often flat cannon trajectories were favored (angle of arrival). Shot fired at above 2º horizontal would likely strike too steeply and would bury itself in the ground on the first impact, limiting the potential damage. Solid shot traveling through a position or column at head or shoulder height could cause extensive damage and numerous casualties. At other times, ricochet fire would reference low charge shot being lobbed just over the parapets with the intention of bouncing or rolling the shot through the defenders behind. The idea here is not to bury the shot, but to keep the shot "moving" as long as possible after the initial impact — illusions to bowling are frequently referenced to ricochet fire. The damage caused by even seemingly slow-moving solid shot is considerable, particularly if striking an individual or a group of individuals.

Any reference to “maximum range” should always send up a red flag. Poorly framed and considered, it can easily mislead both the writer and the reader. Gunpowder stores were too valuable to waste at distances beyond effective range. Even effective ranges can be misleading as those judgments were made based only on the horizontal plane, drift from the left or right of the target line, simulating a column of advancing troops. Estimates of effective ranges were based on the gun being fired with the barrel level or elevated only a very few degrees, not arching fire that would bury the shot. By its very nature, an appreciable elevation in the angle of shot implies a considerable loss in shot velocity. Cannon carriages designs and their reinforcements assumed that most round shot would be fired at 5o or less. Unless the target was massive, even the largest cannon had an effective range of no more than 1,500 yards.

The recognized effective range of cannon was only 40 or 50% of the maximum range. During a siege, the first attacking batteries would often be established just within the effective range of the smallest cannon selected for those batteries, but the initial trenching would be started further away at a safe distance from any defensive fire. However, the attacking force might decide to forego erecting any long-distance batteries entirely and only erect medium and short distant batteries (breaching batteries). Often these first batteries were at or just beyond the effective range of the small-bore cannon possessed by the defending force. Simply put, the first artillery duels would be between the large bore cannon and shell pieces of the attacking force versus the large bore cannon and shell pieces of the defenders.

The maximum range for a 6-pdr or even a light brass 12-pdr was about 1,400 yards. The full-service charge on light brass 12-pdr was only three pounds of powder, one-and-a-half pounds less than a full charge for most 9-pdrs, not the six pounds of powder typical of a heavy or medium 12-pdr (McConnell 1988, Page 392). The 1,000 pound "light" 12-pdr was made possible by having a barrel length of only 5 feet. Using a heavier ball and less powder, the effective range of a light 12-pdr was less than that of a 9-pdr ― about 700 yards and 900 yards, respectively.

The maximum rate of fire for a gun depended on the setting – a siege or a battle. Aboard ship, gun crews were trained for speed in reloading. With so many men working in close quarters, frequent drills were mandatory. The size of a warship crew was determined not by how many men were needed to sail the ship, but how many men were needed to service the guns ― a much higher number. For example, aboard a large warship, a dozen men or more would be assigned to crew each of the 32-pdrs. To many in the Navy, the sheer volume of fire was key in an engagement; these officers wanted guns that could be easily and quickly loaded, so reducing windage to increase accuracy was not in their view desirable if it came at the cost of slowing the rate of fire. Within the Navy, there was concern that lengthy storage at sea might promote rust and metal corrosion, altering the size and shape of the shot; so again, the windage specification should not be too strict. Under the typical noise and dense smoke of a battle, a 12-pdr on a field carriage might fire at an average rate of once per minute, but if hard pressed, the rate of fire could reach four shots per minute, but the ammunition stores would then be quickly exhausted.

In a siege setting, range to target, gunpowder and shot reserves would be key factors in determining the rate of fire. After a battery would fire, the smoke was allowed to fully clear before firing the next round. Siege guns were probably fired no more than about eight to ten times per hour, but gun crews could be pushed to double that rate. The longer ranges involved with the first stages of a siege were inherently less accurate and demanded considerable care with the aim. The need for precise and directed loading was another factor that increased with range ― there was no point in a hurried loading. In a similar vein, knowing the gunpowder and shot reserves had to be husbanded over the long term, slowed the rate of fire. All of these factors negated the desire or need for high rates of fire during a siege; accuracy was strongly favored over other considerations. The standard protocol was to assign each gun a specific number of rounds per day. If gunpowder stores were limited, either side might allocate the vast majority of the gunpowder to the later stages of the siege and only then increase the rate of fire. In many ways, this became a matter of logistics and accounting. Schedules would be set and timetables for work established based on accepted engineering standards. During the early stages, each gun might be assigned a maximum number of rounds per day, ten rounds or less would not be unusual, especially defensive fire. In the latter stages of the siege when the ranges decreased, the rounds assigned per gun might increase to sixty or more per day. Siege gun firing rates could approach or exceed ten per hour, but the guns had to be allowed to cool after 10-12 rounds or the barrel would warp or the vent could enlarge. The cooling could be done via repeated swabbing with water, but resting the gun was an additional precaution. Starting in 1757, the British would include many heavy brass guns in their siege trains including those expeditions in the interior of North America. After 1755 and Braddock, the British in North America were not maneuvering armies, but plodding behemoths, measured and careful. However, the logistic limitations were key and a trenching schedule would be developed to determine how long it would take to establish breaching batteries and ammunition use would then be planned accordingly.

No country could afford to fortify and defend all their cities and fortifications to the point that they were invulnerable to a siege. By the very nature of a siege, the attacker would both outman and outgun the defending force. But all advantages did not lay with the attacker. The true defense against a siege army was not to win the artillery duel. It was simply to holdout long enough to be rescued by an allied army ― to have the siege lifted. The attacker was keenly aware of this possibility and developed his plans and schedules accordingly. The defending force also had the option of sending sorties against attacking positions in hopes of buying more time. It was very much a balancing act on both sides. During the Seven Years' War, siege operations often needed to be done quickly, foregoing any attempt at rescue; aspects of more classical siege operations were often skipped in hopes of saving time. Where and when the British chose to conduct sieges, there was little or no possibility of the siege being lifted by an allied army — Louisbourg (1758), Québec (1759), (Pondicherry, 1760-1761), Belle-Isle (1761), and Havana (1762). These operations were always joint army-naval campaigns, supported by more than ample ordnance.

Mortar and Howitzer Use

If a target was massive in size, the need for accuracy was diminished and high arching artillery employing solid shot was an option. Effective against cities and large towns, against spread armies in the field, it was problematic — the solid shot would most likely simply bury itself in the open earth on first impact. Being non-explosive, any damage would be strictly limited. Under these circumstances, the exploding shells of mortars and howitzers were much more effective.

Mortars and howitzers fired shells fitted with a fuse. Shells were hollow projectiles filled with gunpowder and often some form of shot. Internal to the shell, the gunpowder and shot needed to be isolated from each other or the shell could detonate prematurely — internal frictional forces sparking an explosion. The shell walls were thick metal and greatly contributed to the damage caused by the shell. Aside from standard shells, special formulations were developed that increased the likelihood that fires would develop as a result of the explosion (carcasses).

As it regards Fort Carillon (Ticonderoga), Montcalm's Engineer-in-Chief, M. de Pontleroy, writes

“were I entrusted to the siege of it, I should only require six mortars and two cannon.” (O'Callaghan, Volume X, Page 720).

In a similar vein, M. d'Hugues writes Maréchal de Belle-Isle, Minister of War in Paris. Although a junior officer, d'Hugues assessment reflects his experience serving under Montcalm (O'Callaghan, Vol. X, May 1, 1758, Page 708):

“The forts in this country are ordinarily constructed only of pieces of timber one over another, in which cannon effects a practicable breach with more difficulty than in stone; therefore the forts such as they are now in Canada have been, and will be taken only by the force of shell; this would not be the case had not the bad habit prevailed of building forts too small at points where a place capable of resistance was required.”

Mortars may appear to be simple, but the physics is not. Mortars were not immune to bursting or failure. The lower lip of the bore was subject to severe stress during firing. Long mortar bores might contribute accuracy, but the shell would then repeatedly tumble within the bore generating even more unwanted stress. The size and shape of the powder chamber was a fluid concept and a source of considerable debate and study with the ultimate goal of reducing stress on the bore walls. Howitzers and mortars fired exploding shells with inserted fuses. Ideally, the shells would detonate in mid-air just before or at the instant of hitting the ground. By varying fuse lengths on the shells, some crude control of the timing of the explosion could be achieved. The construction and manufacture of fuses followed very strict protocols (Caruana, 1979). When targeting a gunpowder magazine or any casement, it was hoped that the shell would first penetrate the roof structure before exploding. Alternatively, howitzers could be used in ricochet with the idea the shell would not be buried by arching fire, but neither would it explode prematurely high in the air. The explosion would occur while the shell was still rolling on the ground or had just stopped. Here, damage does not correlate with muzzle velocity or range. Instead, metal shards from the shell casing and the concussive wave of the explosion would cause the damage. For air explosions and the safety of the mortar crew, the minimum workable fuse length for the larger mortars required that the mortar be at least 600 or 700 yards away from the target (Wise and Hook 1979, Page 29). With 8-inch and 10-inch brass mortars, the maximum range was judged to be about 1,600 yards and 1,200 yards, respectively. The much bulkier and heavily reinforced 10-inch iron mortar allowed for a much higher gunpowder charge and had a range of 2,500 yards. The much smaller brass 4 2/5-inch mortar had a maximum range of 800 yards (Hughes 1969, Pages 37; but see Page 100). The brass 5 1/2-inch mortar could reach 1,000 yards.

Often mortars were fired at a fixed angle of 45º. To alter the distance the shell flew, the size of the propellant charge would be varied. Alternatively, the angle on the mortar could be modified using wood wedges. As a large percentage of shells only exploded after hitting the ground, arching mortar fire could lose much of its effectiveness on soft wet ground where a falling shell could burying itself, a condition not uncommon to European battlefields.

The use of fuses made shell distinctly unreliable. In the early part of the 18th century, two fuses would be lit simultaneously, one for the propellant charge, the second for the mortar shell itself. This was inherently dangerous and the crew had to be ready to quickly abandon the mortar if something went wrong. By the late 18th century, some windage (air space) was allowed when fitting the shell into the mortar; then only a single fuse would be lit in hopes the propellant charge would subsequently ignite the shell fuse. At the time of the Seven Years' War the British were utilizing a single fuse and no wadding; whereas, the French continued lighting two separate fuses and used wadding (Muller 1768, Page 155).

If desired, the formulation inside the shell could be modified to promote the formation of fires (carcasses). Mortars were most effective in a siege; they were especially feared when arrayed against cities and structures apt to burn. Bomb ketches were specialized ships fitted with mortars, typically two 13-inch or 10-inch sea-service mortars, but land mortars were used in interior New York and on the Great Lakes ― the British equipped sloops with 8-inch mortars. These sea-service mortars were much more massive than land-service mortars allowing for heavier propellant charges, double the land mortar's weight. These sea-service mortars weighed in at some 9,200 and 4,600 pounds, respectively. The bores were both deeper and thicker. A 13-inch iron sea-service mortar had a range of 4,100 yards with a 10-inch iron sea-service mortar having a range of 3,800 yards — 1,300 yards further than the corresponding land-service mortars (Hughes 1969, Page 37). Bomb ketches were used to reduce coastal fortifications and cities. Loudoun had requested three or four bomb ketches for the Louisbourg expedition. In 1759, the British would employ three bomb ketches against Quebec. Wolfe moved at least four sea service mortars, six additional 13-inch mortars, one 10-inch mortar, and six 32-pdrs to the top of Point aux Pères (opposite to Québec) and established two batteries. Throughout this campaign, the British expended some 18,000 shot for 32-pdrs; 18,350 shot for 24-pdrs; 3,000 13-inch shells; and 2,300 10-inch shells; but only some 1,000 shot for 12-pdrs, and 1,000 8-inch shells. The British used some 3,880 barrels of gunpowder during the Siege of Quebec (Doughty 1901, Appendix II, Page 57).

During the capture of the Citadel on Belle-Isle off the coast of Brittany, the British developed three key artillery batteries (1761). Heavy 24-pdrs and medium 12-pdrs were the principal cannon plus 8-inch and 4 2/5-inch howitzers, but a large number of mortars were employed ― two 13-inch and two 10-inch sea service mortars; two 13-inch, three 10-inch, and six 8-inch land service mortars. Fifteen 5 1/2-inch royal and ten 4 2/5-inch coehorn mortars were also available. Some 1,500 barrels of gunpowder; 17,000 shot; and 12,000 shells were expended (Duncan 1879, Page 233).

References

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Acknowledgments

Ken Dunne for the initial version of this article