The War of the Engineers II

Fort Douaumont (Illustration from Neil Demarco’s The Great War)

THE RIPOSTE

On the other hand, now that the engineers knew what the new shells could do, coming up with a way to counter them was not all that difficult, at least in theory. Basically, the material that formed the carapace of the fort simply had to be made stronger. As with the development of melinite, the trick was figuring out the way to put the theory into practice.

The polygon basically had three components. The walls and the dry moat were simply there to protect the garrison and its weapons and supplies. Inside the walls, therefore, were various storage facilities. Then there were the positions for the guns and for observers to direct the fire, as well as positions enabling the defenders to beat off an infantry assault.

In the original design, hardly any attention had been paid to the structures that were inside the fort. The only exception was where the ammunition for the guns was housed, since an explosion there could be catastrophic. But now, faced with the possibility of highly destructive shells landing inside the fort itself, the engineers were forced into some serious rethinking.

Actually, they were faced with a whole set of problems. On the one hand, they had to figure out what to do with the hundreds of forts that had already been constructed, while on the other they had to make fundamental design changes in the new ones that the defensive scheme called for.

Moreover, each of the three components required a different approach. Without going into even more tedious technical details, the engineers employed a mix of three basic techniques. They developed a sturdier and more resistant concrete, generically referred to as reinforced concrete, that they could test to see that it was proof against the new shells.

Wherever possible, however, they used a much cheaper and even more effective technique: either digging down into the ground or sandwiching earth and masonry. Although the most visible sign of this was thicker walls, what was really going on was that more and more of the structure was subterranean, as that was the easier and most efficient way to protect the interior structures of the fort.

Gradually, therefore, the polygon became simply an enormous hulking mound whose most visible feature was the entrance (at the rear), and the dry moat and wall configuration marking the perimeter.

So far, so good, but there still remained the rather more difficult matter of protecting the guns and their observers. Simply making the walls thicker was not a solution, since the thickness would severely limit the mobility of the gun. So gradually, over the next twenty years, the engineers began to rely more and more on thick iron plates.

In fact, as time passed, the visible surface of one of the newer forts (or one that had been extensively renovated) was beginning to look more like some sort of bizarre naval vessel, with round humps scattered over its surface, some of them looking like squat iron chimneys, others simply bulges.

But upgrading a fort was an expensive proposition, and there was only so much money available for national defense. The parties of the left were more amenable to spending money on fortifications than on arming a professional military, but as the years rolled by, and the modernization of the forts consumed more and more money, the competition increased, with a growing cadre of officers questioning whether the money couldn’t be better spent on weapons, and members of the government wondering whether it was necessary to spend anything at all on national defense.

Given the horrific nature of the war, we sometimes forget the extent to which the elected representatives who formed the governments of the major powers were increasingly of the opinion that wars were obsolete, or impossible, or anyway to be avoided at all costs. And as is usually the case with parliamentary democracies, the result was generally a patched-together compromise that didn’t satisfy anyone. The engineers got enough money to upgrade some forts, and the gunners got enough money to develop a new gun—a compromise that left both groups at odds with each other, and with the government.

THE RECOIL REVOLUTION

As if the widespread adoption of TNP as the preferred explosive material for shells was not enough of a challenge for the beleaguered engineers, by 1897, they were faced with yet another innovation, one that fundamentally transformed the nature of artillery, and had an impact on the battlefield that was even more dramatic.

Although Sir Isaac Newton didn’t work it out as a law until 1687, every gunner realized that when he fired his cannon, the expanding gases generated by the explosion did much more than hurl the cannonball at the enemy. The gases, confined by the cannon barrel, also pushed back. This was a practical example of Newton’s third law, that for every action, there is an equal and opposite reaction. Gunners called it recoil. Fire the gun and it moved backward, shifted position.

Over the centuries the recoil phenomenon got worse, first as the fit of the projectile in the barrel became tighter, and then, with the advent of rifling, breech loading, and TNP, a serious problem.

At first, navies largely were immune, because their guns were mounted directly to the ship itself. Most of us have at least a passing familiarity with the squat four-wheeled gun carriages of sailing vessels. When one of them was fired, it rolled back, was slowed down by its own weight, by the friction of the wheels on the deck, and by cables attached to the carriage.

Much the same principle applied to cannon mounted in forts. The gun mounts connected the carriage directly to a mass of stonework embedded in the earth, and the sheer disproportion of the mass absorbed the energy of the recoil. Provided the gun mount was sturdy enough to take the stress, the gun would remain firmly in place.

But gunners who were required to move their weapons from battle to battle had a bit of a problem. The most practical way to transport a cannon was to mount the gun carriage on wheels and pull it behind a team of horses. But then, when you fired it, those same wheels worked against you, as the gun would move backward, or jump wildly.

As the problem became more acute, gunners came to depend more and more on mechanical devices to keep the gun from moving around each time it was fired. Not only was the movement dangerous to the gunners, but it meant that they had to manhandle it back into position after each round, and aim all over again. The more potent the gun, the worse the problem.

To dampen the recoil, gunners used mechanical wedges, ramps, and dirt—anything and everything that would absorb the energy. But as the range of the guns increased, as indirect fire became the norm, the inherent weakness of mechanical recoil devices became more noticeable. As long as the gunners were aiming directly at the target, simply sighting the gun as if it were a giant musket, the fact that it moved after each round was fired was not much of a problem.

But in indirect fire it was. Even at a relatively short range of, say, 5,000 meters, a one-degree shift in the position of the gun tube from one round to the next would mean that the second round would land nearly 100 meters from the first—and that was assuming the gunners could reposition the gun to within one degree of the initial position. So in actual practice, the margin of error was significant.

So the gunners in a fort had a terrific advantage. They had a fixed field of fire, and could figure out the precise aim necessary to hit any given target well in advance. Or, in other words, they could, through practice, master the terrain, while their opponents couldn’t. Besides, getting a heavy siege gun in position would take a great deal of time. The potency of an explosive like melinite meant that although there had been serious advances in metallurgy over the course of the nineteenth century, gun carriages still had to be extremely heavy, so they could withstand the shock of being fired and absorb some of the recoil. It would hardly do to block the wheels of the gun carriage so it couldn’t move, only to have the barrel fly off when it was fired. Nor would the gunners be enthusiastic about firing such a weapon.

But by 1897, French artillery designers had come up with a truly elegant solution to the problem. The gun tube was resting on a trough, attached to the gun mount by hydraulic cylinders. When the gun was fired, the barrel moved back, the cylinders absorbed the forces generated, and then recoiled, moving the barrel back to exactly the same position.

There were all sorts of advantages to this scheme. The gun tube remained in exactly the same position, indispensable for indirect fire. The gun mount and carriage could be much lighter, since the hydraulic rams absorbed the shock of firing. And since nothing moved, the rate of fire increased dramatically. The new French field gun, the justly legendary 75, could in theory fire 15 rounds per minute, whereas the gun replaced could only manage three.

Suddenly, everybody’s artillery was obsolete. The new French gun, on account of the size of the shell, was the best field gun in the world. And the French army had it: it was lighter and hence more mobile, it had a much higher rate of fire, and its explosive shells had a significantly higher payload of high explosive.

The 75 really was the perfect gun of its type, and neither the Germans nor the Austrians were able to match it. Although by 1914 their standard field gun used the same principle, their weapons were markedly inferior. The 75 is really a fascinating piece of machinery, because generally speaking, devices relying on new technology always have teething problems, and rarely deliver immediately on the claims of their inventors, one reason being a failure on the part of the user to understand what he has.

But here, almost uniquely, was a weapon that sprang forth in perfection, more or less like Athena from the forehead of Zeus. So by 1900, the attitude of French artillery officers, basically, was that they had the perfect weapon, and there was no need to develop more.

The superiority of the 75 was not mythical. It was better than its German counterpart, the 7.7-centimeter field gun, in two key respects: It had a 1,400-meter range advantage firing shrapnel shells, and although the range was the same for both guns when firing high-explosive shells, the French shells contained five times as much explosive as did the German ones (0.650 kilograms as opposed to 0.160 kilograms). The first advantage evaporated fairly quickly, as both sides discovered that high-explosive shells were more effective, but this only emphasized the advantage of the French gun in firing explosive shells, owing to the considerably greater amount of explosive carried.

Had the armies of 1914 and after relied exclusively on fieldpieces of less than 80 millimeters, the French would have had a tremendous superiority, and a good many analysts seem to believe that this was the case, writing as though these guns were the mainstays of German and French divisional artillery. Unfortunately for the French, the battlefields of 1914–1918 would be controlled by a combination of heavy artillery, field howitzers, and infantry guns, principally mortars.

But the French put all their faith in the 75. In 1914, a French army corps had 120 of them. A German army corps had only 108 7.7-centimeter field guns. But in addition it deployed 36 10.5– and 16 15.0-centimeter howitzers. When the American army began doing tests, they found that at distances from two to three thousand meters, the howitzer was two and a half times as accurate as the 75-millimeter field gun, and that over the practical range of both weapons, the howitzer would always do significantly more damage than the field gun. Multiplying out the values obtained by the American experiments suggests that each German infantry division had as much killing power in its 105-millimeter howitzers as did all the artillery of a French division. Given that enormous advantage, a German army corps simply outgunned its French (or British) counterpart.

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