Pedreros (fig. 23c) were comparatively light. The foundryman used only half the metal he would put into a culverin, for the stone projectile weighed only a third as much as an iron ball of the same size, and the bore walls could therefore be comparatively thin. They were made in calibers up to 50-pounders. There was a chamber for the powder charge and little danger of the gun"s bursting, unless a foolhardy fellow loaded it with an iron ball. The wall thicknesses of this gun are shown in Figure 24, where the inner circle represents the diameter of the chamber, the next arc the bore caliber, and the outer lines the respective diameters at chase, trunnions, and vent.
[Ill.u.s.tration: Figure 24--HOW MUCH METAL WAS IN EARLY GUNS? The charts compare the wall diameters of sixteenth-seventeenth century types. The center circle represents the bore, while the three outer arcs show the relative thickness of the bore wall at (1) the smallest diameter of the chase, (2) at the trunnions, and (3) at the vent. The small arc inside the bore indicates the powder chamber found in the pedrero and mortar.]
Mortars (fig. 23d) were excellent for "putting great fear and terror in the souls of the besieged." Every night the mortars would play upon the town: "it keeps them in constant turmoil, due to the thought that some ball will fall upon their house." Mortars were designed like pedreros, except much shorter. The convenient way to charge them was with _saquillos_ (small bags) of powder. "They require," said Collado, "a larger mouthful than any other pieces."
Just as children range from slight to stocky in the same family, there are light, medium, or heavy guns--all bearing the same family name.
The difference lies in how the piece was "fortified"; that is, how thick the founder cast the bore walls. The English language has inelegantly descriptive terms for the three degrees of "fortification": (1) b.a.s.t.a.r.d, (2) legitimate, and (3) double-fortified. The thicker-walled guns used more powder. Spanish double-fortified culverins were charged with the full weight of the ball in powder; four-fifths that amount went into the legitimate, and only two-thirds for the b.a.s.t.a.r.d culverin. In a short culverin (say, 24 calibers long instead of 30), the gunner used 24/30 of a standard charge.
The yardstick for fortifying a gun was its caliber. In a legitimate culverin of 6-inch caliber, for instance, the bore wall at the vent might be one caliber (16/16 of the bore diameter) or 6 inches thick; at the trunnions it would be 10/16 or 4-1/8 inches, and at the smallest diameter of the chase, 7/16 or 2-5/8 inches. This table compares the three degrees of fortification used in Spanish culverins:
Wall thickness in 8ths of caliber Vent Trunnion Chase
b.a.s.t.a.r.d culverin 7 5 3 Legitimate culverin 8 5-1/2 3-1/2 Double-fortified culverin 9 6-1/2 4
As with culverins, so with cannon. This is Collado"s table showing the fortification for Spanish cannon:
Wall thickness in 8ths of caliber Vent Trunnion Chase Canon sencillo (light cannon) 6 4-1/2 2-1/2 Canon comun (common cannon) 7 5 3-1/2 Canon reforzado (reinforced cannon) 8 5-1/2 3-1/2
Since cast iron was weaker than bronze, the walls of cast-iron pieces were even thicker than the culverins. Spanish iron guns were founded with 300 pounds of metal for each pound of the ball, and in lengths from 18 to 20 calibers. English, Irish, and Swedish iron guns of the period, Collado noted, had slightly more metal in them than even the Spaniards recommended.
[Ill.u.s.tration: Figure 25--SIXTEENTH CENTURY CHAMBERED CANNON.
a--"Bell-chambered" demicannon, b--Chambered demicannon.]
Another way the designers tried to gain strength without loading the gun with metal was by using a powder chamber. A chambered cannon (fig.
25b) might be fortified like either the light or the common cannon, but it would have a cylindrical chamber about two-thirds of a caliber in diameter and four calibers long. It was not always easy, however, to get the powder into the chamber. Collado reported that many a good artillerist dumped the powder almost in the middle of the gun. When his ladle hit the mouth of the chamber, he thought he was at the bottom of the bore! The cylindrical chamber was somewhat improved by a cone-shaped taper, which the Spaniards called _encampanado_ or "bell-chambered." A _canon encampanado_ (fig. 25a) was a good long-range gun, strong, yet light. But it was hard to cut a ladle for the long, tapered chamber.
Of all these guns, the reinforced cannon was one of the best. Since it had almost as much metal as a culverin, it lacked the defects of the chambered pieces. A 60-pounder reinforced cannon fired a convenient 55-pound ball, was easy to move, load, and clean, and held up well under any kind of service. It cooled quickly. Either cannon powder or fine powder (up to two-thirds the ball"s weight) could be used in it.
Reinforced cannon were an important factor in any enterprise, as King Philip"s famed "Twelve Apostles" proved during the Flanders wars.
_Fortification of sixteenth and seventeenth century guns_
------------------------+-------------------------+--------------------- Thickness of bore wall in 8ths of the caliber Spanish Guns +-------+---------+-------+ English guns Vent Trunnions Chase ------------------------+-------+---------+-------+---------------------
Light cannon; bell-chambered cannon 6 4-1/2 2-1/2 b.a.s.t.a.r.d cannon.
Demicannon 6 5 3 Common cannon; common siege cannon 7 5 3-1/2 Light culverin; common battering cannon 7 5 3 b.a.s.t.a.r.d culverin; legitimate cannon.
Common culverin; reinforced cannon 8 5-1/2 3-1/2 Legitimate culverin; double-fortified cannon.
Legitimate culverin 9 6-1/2 4 Double-fortified culverin.
Cast-iron cannon 10 8 5 Pasavolante 11-1/2 8-1/2 5-1/2 ------------------------+-------+---------+-------+---------------------
While there was little real progress in mobility until the days of Gustavus Adolphus, the wheeled artillery carriage seems to have been invented by the Venetians in the fifteenth century. The essential parts of the design were early established: two large, heavy cheeks or side pieces set on an axle and connected by transoms. The gun was cradled between the cheeks, the rear ends of which formed a "trail"
for stabilizing and maneuvering the piece.
Wheels were perhaps the greatest problem. As early as the 1500"s carpenters and wheelwrights were debating whether dished wheels were best. "They say," reported Collado, "that the [dished] wheel will never twist when the artillery is on the march. Others say that a wheel with spokes angled beyond the cask cannot carry the weight of the piece without twisting the spoke, so the wheel does not last long.
I am of the same opinion, for it is certain that a perpendicular wheel will suffer more weight than the other. The defect of twisting under the pieces when on the march will be remedied by making the cart a little wider than usual." However, advocates of the dished wheel finally won.
SMOOTHBORES OF THE LATER PERIOD
From the guns of Queen Elizabeth"s time came the 6-, 9-, 12-, 18-, 24-, 32-, and 42-pounder cla.s.sifications adopted by Cromwell"s government and used by the English well through the eighteenth century. On the Continent, during much of this period, the French were acknowledged leaders. Louis XIV (1643-1715) brought several foreign guns into his ordnance, standardizing a set of calibers (4-, 8-, 12-, 16-, 24-, 32-, and 48-pounders) quite different from Henry II"s in the previous century.
The cannon of the late 1600"s was an ornate masterpiece of the foundryman"s art, covered with escutcheons, floral relief, scrolls, and heavy moldings, the most characteristic of which was perhaps the banded muzzle (figs. 23b-c, 25, 26a-b), that bulbous bit of ornamentation which had been popular with designers since the days of the bombards. The flared or bell-shaped muzzle (figs. 23a, 26c, 27), did not supplant the banded muzzle until the eighteenth century, and, while the flaring bell is a usual characteristic of ordnance founded between 1730 and 1830, some banded-muzzle guns were made as late as 1746 (fig. 26a).
By 1750; however, design and construction were fairly well standardized in a gun of much cleaner line than the cannon of 1650.
Although as yet there had been no sharp break with the older traditions, the shape and weight of the cannon in relation to the stresses of firing were becoming increasingly important to the men who did the designing.
Conditions in eighteenth century England were more or less typical: in the 1730"s Surveyor-General Armstrong"s formulae for gun design were hardly more than continuations of the earlier ways. His guns were about 20 calibers long, with these outside proportions:
1st reinforce = 2/7 of the gun"s length.
2d reinforce = 1/7 plus 1 caliber.
chase = 4/7 less 1 caliber.
The trunnions, about a caliber in size, were located well forward (3/7 of the gun"s length) "to prevent the piece from kicking up behind" when it was fired. Gunners blamed this bucking tendency on the practice of centering the trunnions on the _lower_ line of the bore.
"But what will not people do to support an old custom let it be ever so absurd?" asked John Muller, the master gunner of Woolwich. In 1756, Muller raised the trunnions to the _center_ of the bore, an improvement that greatly lessened the strain on the gun carriage.
[Ill.u.s.tration: Figure 26--EIGHTEENTH CENTURY CANNON, a--Spanish bronze 24-pounder of 1746. b--French bronze 24-pounder of the early 1700"s. c--English iron 6-pounder of the middle 1700"s. The 6-pounder is part of the armament at Castillo de San Marcos.]
[Ill.u.s.tration: Figure 27--SPANISH 24-POUNDER CAST-IRON GUN (1693).
Note the modern lines of this cannon, with its flat breech and slight muzzle swell.]
The caliber of the gun continued to be the yardstick for "fortification"
of the bore walls:
Vent 16 parts End of 1st reinforce 14-1/2 do Beginning of second reinforce 13-1/2 do End of second reinforce 12-1/2 do Beginning of chase 11-1/2 do End of chase 8 do
For both bronze and iron guns, the above figures were the same, but for bronze, Armstrong divided the caliber into 16 parts; for iron it was only 14 parts. The walls of an iron gun thus were slightly thicker than those of a bronze one.
This eighteenth century cannon was a cast gun, but hoops and rings gave it the built-up look of the barrel-stave bombard, when hoops were really functional parts of the cannon. Reinforces made the gun look like "three frustums of cones joined together, so as the lesser base of the former is always greater than the greatest of the succeeding one." Ornamental fillets, astragals, and moldings, borrowed from architecture, increased the illusion of a sectional piece. Tests with 24-pounders of different lengths showed guns from 18 to 21 calibers long gave generally the best performance, but what was true for the 24-pounder was not necessarily true for other pieces. Why was the 32-pounder "bra.s.s battering piece" 6 inches longer than its 42-pounder brother? John Muller wondered about such inconsistencies and set out to devise a new system of ordnance for England.
Like many men before him, Muller sought to increase the caliber of cannon without increasing weight. He managed it in two ways: he modified exterior design to save on metal, and he lessened the powder charge to permit shortening and lightening the gun. Muller"s guns had no heavy reinforces; the metal was distributed along the bore in a taper from powder chamber to muzzle swell. But realizing man"s reluctance to accept new things, he carefully specified the location and size for each molding on his gun, protesting all the while the futility of such ornaments. Not until the last half of the next century were the experts well enough versed in metallurgy and interior ballistics to slough off all the useless metal.
So, using powder charges about one-third the weight of the projectile, Muller designed 14-caliber light field pieces and 15-caliber ship guns. His garrison and battering cannon, where weight was no great disadvantage, were 18 calibers long. The figures in the table following represent the princ.i.p.al dimensions for the four types of cannon--all cast-iron except for the bronze siege guns. The first line in the table shows the length of the cannon. To proportion the rest of the piece, Muller divided the shot diameter into 24 parts and used it as a yardstick. The caliber of the gun, for instance, was 25 parts, or 25/24th of the shot diameter. The few other dimensions--thickness of the breech, length of the gun before the barrel began its taper, fortification at vent and chase--were expressed the same way.
-----------------------------------+-------+--------+-------+--------- | Field | Ship | Siege | Garrison -----------------------------------+-------+--------+-------+--------- Length in calibers | 14 | 15 | 18 | 18 (Other proportions in 24ths of the shot diameter) | Caliber | 25 | 25 | 25 | 25 Thickness of breech | 14 | 24 | 16 | 24 Length from breech to taper | 39 | 49 | 40 | 49 Thickness at vent | 16 | 25 | 18 | 25 Thickness at muzzle | 8 | 12-1/2 | 9 | 12-1/2 -----------------------------------+-------+--------+-------+---------
The heaviest of Muller"s garrison guns averaged some 172 pounds of iron for every pound of the shot, while a ship gun weighed only 146, less than half the iron that went into the sixteenth century cannon.
And for a seafaring nation such as England, these were important things. Perhaps the opposite table will give a fair idea of the changes in English ordnance during the eighteenth century. It is based upon John Muller"s lists of 1756; the "old" ordnance includes cannon still in use during Muller"s time, while the "new" ordnance is Muller"s own.
Windage in the English gun of 1750 was about 20 percent greater than in French pieces. The English ratio of shot to caliber was 20:21; across the channel it was 26:27. Thus, an English 9-pounder fired a 4.00-inch ball from a 4.20-inch bore; the French 9-pounder ball was 4.18 inches and the bore 4.34.
The English figured greater windage was both convenient and economical: windage, said they, ought to be just as thick as the metal in the gunner"s ladle; standing shot stuck in the bore and unless it could be loosened with the ladle, had to be fired away and lost. John Muller brushed aside such arguments impatiently. With a proper wad over the shot, no dust or dirt could get in; and when the muzzle was lowered, said Muller, the shot "will roll out of course." Besides, compared with increased accuracy, the loss of a shot was trifling.
Furthermore, with less room for the shot to bounce around the bore, the cannon would "not be spoiled so soon." Muller set the ratio of shot to caliber as 24:25.
_Calibers and lengths of princ.i.p.al eighteenth century English cannon_
---------+-----------+---------------------+-----------+----------+ Caliber | Field | Ship | Siege | Garrison | +-----------+----------+----------+-----------+----------+ | Iron | Bronze | Iron | Bronze | Iron | +-----+-----+----+-----+-----+----+-----+-----+----+-----+ (pounder)| Old | New | Old| New | Old | New| Old | New | Old| New | ---------+-----+-----+----+-----+-----+----+-----+-----+----+-----+ 1-1/2 | | | | | | | 6"0"| | | | 3 |3"6" |3"3" | |3"6" | 4"6"|3"6"| 7"0"| |4"6"| 4"2"| 4 | | | | | 6"0"| | | | | | 6 |4"6" |4"1" |8"0"|4"4" | 7"0"|4"4"| 8"0"| |6"6"| 5"3"| 9 | |4"8" | |5"0" | 7"0"|5"0"| 9"0"| |7"0"| 6"0"| 12 |5"0" |5"1" |9"0"|5"6" | 9"0"|5"6"| 9"0"| 6"7"|8"0"| 6"7"| 18 | |5"10"| |6"4" | 9"0"|6"4"| 9"6"| 8"4"|9"0"| 7"6"| 24 |5"6" |6"5" |9"6"|7"0" | 9"0"|7"0"| 9"6"| 8"4"|9"0"| 8"4"| 32 | | | |7"6" | 9"6"|7"6"|10"0"| 9"2"|9"6"| 9"2"| 36 | | | |7"10"| | | | 9"6"| | | 42 | | |9"6"|8"4" |10"0"|8"4"| 9"6"|10"0"| |10"0"| 48 | | | |8"6" | |8"6"| |10"6"| | | ---------+-----+-----+----+-----+-----+----+-----+-----+----+-----+
In the 1700"s cast-iron guns became the princ.i.p.al artillery afloat and ash.o.r.e, yet cast bronze was superior in withstanding the stresses of firing. Because of its toughness, less metal was needed in a bronze gun than in a cast-iron one, so in spite of the fact that bronze is about 20 percent heavier than iron, the bronze piece was usually the lighter of the two. For "position" guns in permanent fortifications where weight was no disadvantage, iron reigned supreme until the advent of steel guns. But non-rusting bronze was always preferable aboard ship or in seacoast forts.
Muller strongly advocated bronze for ship guns. "Notwithstanding all the precautions that can be taken to make iron Guns of a sufficient strength," he said, "yet accidents will sometimes happen, either by the mismanagement of the sailors, or by frosty weather, which renders iron very brittle." A bronze 24-pounder cost 156, compared with 75 for the iron piece, but the initial saving was offset when the gun wore out. The iron gun was then good for nothing except sc.r.a.p at a farthing per pound, while the bronze cannon could be recast "as often as you please."