The Evolution of Naval Armament

by Frederick Leslie Robertson

We have traced the smooth-bore cannon through the successive stages of its evolution. It is now proposed to give, in the form of a biographical sketch, an account of the inception of scientific methods as applied to its use, and at the same time to pay some tribute to the memory of the man who laid the foundations deep and true of the science of modern gunnery. One man was destined to develop, almost unaided, the principles of gunnery as they are known to-day. This man was a young Quaker of the eighteenth century, Benjamin Robins.

For a variety of reasons his fame and services seem never to have been sufficiently recognized or acknowledged by his own countrymen. To many his name is altogether unknown. To some it is associated solely with the discovery of the ballistic pendulum: the ingenious instrument by which, until the advent of electrical apparatus, the velocities of bullets and cannon balls could be measured with a high degree of accuracy. But the ballistic pendulum was, as we shall see, only one manifestation of his great originating power. The following notes will show to what a high place Robins attained among contemporary thinkers; and demonstrate the extent to which, by happy combination of pure reason and experiment, he influenced the development of artillery and fire-arms. His New Principles of Gunnery constituted a great discovery, simple and surprisingly complete. In this work he had not merely to extend or improve upon the inventive work of others; his first task was to expose age-long absurdities and demolish all existing theories; and only then could he replace them by true principles founded on correct mathematical reasoning and confirmed by unwearying experiment with a borrowed cannon or a “good Tower musquet.”

Down to the time of Robins, gunnery was still held to be an art and a mystery. The gunner, that honest and godly man,[80] learned in arithmetic and astronomy, was master of a terrible craft;—his saltpetre gathered, it was said, from within vaults, tombs, and other desolate places;—his touchwood made from old toadstools dried over a smoky fire;—himself working unscathed only by grace of St. Barbara, the protectress of all artillerymen. The efficiency of his practice depended overwhelmingly on his own knowledge and on the skill with which he mixed and adjusted his materials. No item in his system was of sealed pattern; every element varied between the widest limits. There were no range-tables. His shots varied in size according to the time they happened to have been in service, to the degree of rusting and flaking which they had suffered, and to their initial variations in manufacture. His piece might be bored taper; if so, and if smaller at the breech end than at the muzzle, there was a good chance of some shot being rammed short of the powder, leaving an air space, so that the gun might burst on discharge; if smaller at the muzzle end the initial windage would be too great, perhaps, to allow of efficient discharge of any shot which could be entered. There was always danger to be apprehended from cracks and flaws.

But the greatest of mysteries was that in which the flight of projectiles was shrouded. At this point gunnery touched one of the oldest and one of the main aspects of natural philosophy.

The Greek philosophers failed, we are told, in spite of their great mental subtlety, to arrive at any true conception of the laws governing the motion of bodies. It was left to the period of the revival of learning which followed the Middle Ages to produce ideas which were in partial conformity with the truth. Galileo and his contemporaries evolved the theory of the parabolic motion of falling bodies and confirmed this brilliant discovery by experiment. Tartaglia sought to apply it to the motion of balls projected from cannon, but was held up by the opposing facts: the initial part of the trajectory was seen to be a straight line in actual practice, and even, perhaps, to have an upward curvature. So new hypotheses were called in aid, and the path of projectiles was assumed to consist of three separate motions: the motus violentus, the motus mixtus, and the motus naturalis. During the motus violentus the path of the spherical projectile was assumed to be straight—and this fallacy, we may note in passing, gave rise to the erroneous term “point blank,” to designate the distance to which the shot would travel before gravity began to operate; during the motus naturalis the ball was assumed to fall along a steep parabola; and during the motus mixtus, the path of the trajectory near its summit, the motion was assumed to be a blend of the other two. This theory, though entirely wrong, fitted in well with practical observation; the trajectory of a spherical shot was actually of this form described. But in many respects it had far-reaching and undesirable consequences. Not only did it give rise to the misconception of the point en blanc; it tended to emphasize the value of heavy charges and high muzzle velocities while at the same time obscuring other important considerations affecting range.

So the gunner was primed with a false theory of the trajectory. But even this could not be relied on as constant in operation. The ranging of his shot was supposed to be affected by the nature of the intervening ground; shot were thought to range short, for some mysterious reason, when fired over water or across valleys, and the gunner had to correct, as best he could, for the extra-gravitational attraction which water and valleys possessed. In addition to all these bewilderments there was the error produced by the fact that the gun itself was thicker at the breech than at the muzzle, so that the “line of metal” sight was not parallel with the bore: a discrepancy which to the lay mind, and not infrequently to the gunner himself, was a perpetual stumbling-block.

It is not surprising that, in these conditions, the cannon remained a singularly inefficient weapon. Imperfectly bored; discharging a ball of iron or lead whose diameter was so much less than its own bore that the projectile bounded along it and issued from the muzzle in a direction often wildly divergent from that in which the piece had been laid; on land it attained its effects by virtue of the size of the target attacked, or by use of the ricochet; at sea it seldom flung its shot at a distant ship, except for the purpose of dismasting, but, aided by tactics, dealt its powerful blows at close quarters, double-shotted and charged lavishly, with terrible effect. It was then that it was most efficient.

Nor is it surprising that, in an atmosphere of ignorance as to the true principles governing the combustion of gunpowder and the motion of projectiles, false “systems” flourished. The records of actual firing results were almost non-existent. Practitioners and mathematicians, searching for the law which would give the true trajectories of cannon balls, found that the results of their own experience would not square with any tried combination of mathematical curves. They either gave up the search for a solution, or pretended a knowledge which they were unwilling to reveal.

§

In the year 1707 Robins was born at Bath. Studious and delicate in childhood, he gave early proof of an unusual mathematical ability, and the advice of influential friends who had seen a display of his talents soon confirmed his careful parents in the choice of a profession for him: the teaching of mathematics. Little, indeed, did the devout Quaker couple dream, when the young Benjamin took coach for London with this object in view, that their son was destined soon to be the first artillerist in Europe.