Chapter 8

The problem of protecting our people and property from such attacks is not a new one, and, in fact, most of the conditions of this problem remain the same as they were fifty years ago, the differences being in degree rather than in kind. The most natural thought would be to meet such a fleet by another fleet, but the folly of such a course will become apparent from a moment's consideration. The difficulties would be:

1st. Our fleet must be decidedly stronger than that of the enemy, or we simply fight a duel with an equal chance of success or failure.

2d. In such a duel the enemy would risk nothing but the loss of his fleet, and even a portion of that would be likely to escape, but we would not only risk a similar loss, but we would also lose the city or subject it to the payment of a heavy contribution to the enemy.

3d. Unless we have a fleet for every harbor, it would be impossible to depend upon this kind of defense, as the enemy would select whichever harbor he found least prepared to receive him. It would be of vital importance that we defend every harbor of importance, as a neglect to do so would be like locking some of our doors and leaving the others open to the burglars.

4th. It might be thought that we could send our fleet to intercept the enemy or blockade him in his own ports, but this has been found impracticable. Large fleets can readily escape from blockaded harbors, or elude each other on the high seas, and any such scheme implies that we are much stronger on the ocean than the enemy, which is very far from the case. To build a navy that would overmatch that of Great Britain alone would not only cost untold millions, but it would require many years for its accomplishment; and even if this were done, there would be nothing unusual in an alliance of two or more powerful nations, which would leave us again in the minority. _Fleets, then, cannot be relied on for permanent defense_.

Again, it may be said that we have millions of the bravest soldiers in the world who could be assembled and placed under arms at a few days' notice. This kind of defense would also prove a delusion, for a hundred acres of soldiers armed with rifles and field artillery would be powerless to drive away even the smallest ironclad or stop a single projectile from one. In fact, neither of these plans, nor both together, would be much more effective than the windmills and proclamations which Irving humorously describes as the means adopted by the early Dutch governors of New York to defend that city against the Swedes and Yankees.

Having considered some of the means of defense that will _not_ answer the purpose, we may inquire what means _will be_ effective. And here it should be noted that our defenses should be so effective as not only to be reasonably safe, but to be so recognized by all nations, and thus discourage, if not actually prevent, an attack upon our coast.

In the first place, we must have heavy guns in such numbers and of such sizes as to overmatch those of any fleet likely to attack us. These guns must be securely mounted, so as to be worked with facility and accuracy, and they must be protected from the enemy's projectiles at least as securely as his guns are from ours. Merely placing ourselves on equal terms with the enemy, as in case of a duel or an ancient knight's tournament, will not answer, first, because such a state of things would invite rather than discourage attack, and secondly, because the enemy would have vastly more to gain by success and vastly less to lose by failure than we would. This can be accomplished much easier than is generally supposed, either by earthen parapets of sufficient thickness or by iron turrets or casements. It is evident that the weight of metal used in these structures may be vastly greater than could be carried on shipboard. Great weight of metal is no objection on land, but, aside from its cost, is a positive advantage. This is evident when we consider the enormous quantity of energy stored in the larger projectiles moving at high velocities. For example, we often hear of the sixteen inch rifle whose projectile weighs about one ton, and this enormous mass projected at a velocity of 2,000 feet per second would have a kinetic energy of 60,000 foot tons, or it would strike a blow equal to that of ten locomotives of 50 tons each running at 60 miles an hour and striking a solid wall. Any structure designed to resist such ponderous blows must, therefore, have enormous weight, or it will be overturned or driven bodily from its foundations. If the armor itself is not thick enough to give the required weight as well as resistance to penetration, the additional stability must be supplied by re-enforcing it with heavy masses of metal or masonry. It is evident, therefore, that _quality_ of metal is less important than _quantity_, and that so long as it is sufficiently tough to resist fracture, a soft, cheap metal, like wrought iron or low steel, is better adapted for permanent works than any of the fancy kinds of armor that have been tested for naval purposes. As an illustration of this, we may compare compound or steel-faced armor with wrought iron as follows: The best of the former offers only about one-third greater resistance to penetration than the latter, or 12 inches of compound armor may equal 16 inches of wrought iron, but the cost per ton is nearly double; so that by using wrought iron we may have double the thickness, or 24 inches, which would give more than double the resistance to penetration, in addition to giving double the stability against overturning or being driven bodily out of place. But our guns may be reasonably well protected by earthen parapets without any expensive armor by so mounting them that when fired they will recoil downward or to one side, so as to come below the parapet for loading. This method of mounting is called the disappearing principle, and has been suggested by many engineers, some of whose designs date back more than one hundred years. We may also mount our guns in deep pits, where they will be covered from the enemy's guns, and fire them at high elevation, so that the shell will fall from a great height and penetrate the decks of the enemy's ships. This is known as mortar firing, but the modern ordnance used for this purpose is more of a howitzer than a mortar, being simply short rifled pieces arranged for breech loading. All our batteries should, of course, be as far from the city or other object to be protected as possible, to prevent the enemy from firing over and beyond the batteries into the city.

But, with all these precautions, the enemy might put on all steam and run by us either at night or in a dense fog, and we must have some means of holding him under the fire of our guns until his ships can be disabled or driven away. This object is sought to be accomplished by the use of torpedoes anchored in the channels and under the fire of our guns, so that they cannot be removed by the enemy. These torpedoes are generally exploded by electricity from batteries located in casements on shore, these casements being connected with the torpedoes by submarine cables. It is easy to see how the torpedo may be so arranged that when struck by a ship the electric current will be closed, and, if the battery on shore is connected at the same instant, an explosion will take place; on the other hand, if the battery on shore is disconnected a friendly ship may pass in safety over the torpedoes. Many ingenious contrivances have also been devised by which the torpedo may be made to signal back to the shore station either that it has been struck or that it is in good order for service, in case the enemy should undertake to run over it. One simple plan for this is to have a small telephone in the torpedo with some loose buckshot on the diaphragm, which is placed in a horizontal position, and will be slightly tilted as the torpedo is moved about by the waves. By connecting the shore end of the cable with a telephone receiver, the rolling of the shot may be distinctly heard if the torpedo is floating properly, but if sunk at its moorings, or if the cable is broken, no sound will be heard.

The use of torpedoes involves the use of both electricity and high explosives, and a careful study based upon actual experiments has been carried on for many years, by the engineers and naval officers in all civilized countries. Some of these experiments have supplied interesting and useful data, for the use of the agents in question, for various industrial purposes.

Another form of torpedo is that known as the locomotive torpedo, of which there are several kinds; some are propelled by liquid carbonic acid, which is carried in a strong tank and acts through a compact engine in driving the propeller. One of these is steered by electricity from the shore, and is known as the Lay-Haight torpedo, and can run twenty-five miles per hour. The Whitehead torpedo is also propelled by liquid carbonic acid, but is not steered from shore. Its depth is regulated by an automatic device actuated by the pressure of the water. The Howell torpedo is driven by a heavy fly wheel which is set in rapid rotation just before the torpedo is launched. It has but a short range and is intended for launching from ships. Another torpedo is propelled and steered from shore by rapidly pulling out of it two fine steel wires which, in unwinding, drive the twin screw propellers. This is the Brennan torpedo. The Sims-Edison torpedo is both propelled and steered by electricity from the shore, transmitted to a motor and steering relay in the torpedo by an insulated cable. This cable has two cores and is paid out by the torpedo as it travels through the water just as a spider pays out its web. The cable is about half an inch in diameter and two miles long, and the torpedo can be driven at about eighteen miles per hour with a current of thirty amperes and 1,800 volts pressure.

Still another auxiliary weapon of defense is the dynamite gun, or rather, a pneumatic gun, that throws long projectiles carrying from 250 to 450 pounds of dynamite, to a distance of about two miles. The shells are arranged to explode soon after striking the water, by an ingenious battery that ignites the fuse as soon as the salt water enters it. The gun, which is known as the Zalinski gun, is some sixty feet long and fifteen inches in caliber, the compressed air being suddenly admitted to it from the reservoirs at any desired pressure by a special form of valve that regulates the range. These guns are to be mounted in deep pits and fired at somewhat higher elevations than ordinary guns, but it has great accuracy within reasonable limits of range.

FIELD FORTIFICATIONS.

In field fortification an enormous quantity of work was done during our last war. Washington, Richmond, Nashville, Petersburg, Norfolk, New Berne, Plymouth, Vicksburg, and many other cities were elaborately fortified by field works which involved the handling of vast quantities of earth, and, where the opposing lines were near together, ditches, abbatis, ground torpedoes, and wire entanglements were freely used. In some cases the same ground was fortified in succession by both armies, so that the total amount of work expended, in this way, would have built several hundred miles of railway. Around Richmond and Petersburg alone the development of field works was far greater than Wellington's celebrated lines at Torres Vedras. In all future wars, when large armies are opposed to each other, it is probable that field works will play even a more important part than in the past. The great advantage of such works, since the introduction of the deadly breech loading rifles and machine guns, was shown at Plevna, where the Russians were almost annihilated in attempting to capture the Turkish intrenchments.

SIEGES.

It is not proposed to go into historical or other details of this branch of the subject, but to give in a condensed form some account of siege operations. According to the text books, the first thing to be done, if possible, in case of a regular siege, is to "invest" the fortress. This is done by surrounding it as quickly as possible with a continuous line of troops, who speedily intrench themselves and mount guns bearing outward on all lines of approach to the fortress, to prevent the enemy from sending in supplies or re-enforcements. As this line must be at considerable distance from the fort, it is usually quite long, and so is its name, for it is called the line of "Circumvallation." Inside of this line is then established a similar line facing toward the fort, to prevent sorties by the garrison. This line is called the line of "Countervallation," and should be as close to the fort as the range of its guns and the nature of the ground will permit. From this line the troops rush forward at night and open the trenches, beginning with what is called the first parallel, which should be so laid out as to envelop those parts of the fort which are to be made the special objects of attack. From this first parallel a number of zigzag trenches are started toward the fort and at proper intervals other parallels, batteries, and magazines are built; this method of approach being continued until the besieged fort is reached, or until such batteries can be brought to bear upon it as to breech the walls and allow the attacking troops to make an assault.

During these operations of course many precautions must be observed, both by the attacking and defending force, to annoy each other and to prevent surprise, and the work is mostly carried on under cover of the earth thrown from the trenches. These operations were supposed to occupy, under normal conditions, about forty-one days, or rather nights, as most of the work is done after dark, at the end of which time the fort should be reduced to such a condition that its commander, having exhausted all means of defense, would be justified in considering terms of surrender.

The _Theoretical Journal_ of the siege prescribes just what is to be done each day by both attack and defense up to the final catastrophe, and this somewhat discouraging outlook for the defenders was forcibly illustrated by the late Captain Derby, better known by the reading public as "John Phoenix," who, when a cadet, was called upon by Professor Mahan to explain how he would defend a fort, mounting a certain number of guns and garrisoned by a certain number of men, if besieged by an army of another assumed strength in men and guns, replied:

"I would immediately evacuate the fort and then besiege it and capture it again in forty-one days."

Of course the fallacy of this reasoning was in the fact that the besieging army is generally supposed to be four or five times as large as the garrison of the fort; the primary object of forts being to enable a small force to hold a position, at least for a time, against a much larger force of the enemy.

Sieges have changed with the development of engines of war, from the rude and muscular efforts of personal prowess like that described in Ivanhoe, where the Black Knight cuts his way through the barriers with his battle axe, to such sieges as those at Vicksburg, Petersburg, and Plevna, where the individual counted for very little, and the results depended upon the combined efforts of large numbers of men and systematic siege operations. It should also be noticed that modern sieges are not necessarily hampered by the rules laid down in text books, but vary from them according to circumstances.

For example, many sieges have been carried to successful issues without completely investing or surrounding the fortress. This was the case at Petersburg, where General Lee was entirely free to move out, or receive supplies and re-enforcements up to the very last stages of the siege. In other cases, as at Fort Pulaski, Sumter, and Macon, the breeching batteries were established at very much greater distances than ever before attempted, and the preliminary siege operations were very much abbreviated and some of them omitted altogether. This is not an argument against having well defined rules and principles, but it shows that the engineer must be prepared to cut loose from old rules and customs whenever the changed state of circumstances requires different treatment.

MILITARY BRIDGES.

In the movement of armies, especially on long marches in the enemy's country, one of the greatest difficulties to be overcome is the crossing of streams, and this is usually done by means of portable bridges. These may be built of light trestles with adjustable legs to suit the different depths, or of wooden or canvas boats supporting a light roadway wide enough for a single line of ordinary wagons or artillery carriages. The materials for these bridges, which are known as Ponton Bridges, are loaded upon wagons and accompany the army on its marches, and when required for use the bridge is rapidly put together, piece by piece, in accordance with fixed rules, which constitute, in fact, a regular drill. The wooden boats are quite heavy and are used for heavy traffic, but for light work, as, for example, to accompany the rapid movements of the cavalry, boats made of heavy canvas, stretched upon light wooden frames, that are put together on the spot, are used.

During Gen. Sherman's memorable Georgia campaign and march to the sea, over three miles of Ponton bridges were built in crossing the numerous streams met with, and nearly two miles of trestle bridges. In Gen. Grant's Wilderness campaign the engineers built not less than thirty-eight bridges between the Rappahannock and the James Rivers, these bridges aggregating over 6,600 feet in length. Under favorable circumstances such bridges can be built at the rate of 200 to 300 feet per hour, and they can be taken up at a still more rapid rate. When there is no bridge train at hand the engineer is obliged to use such improvised materials as he can get; buildings are torn down to get plank and trees are cut to make the frame. Sometimes single stringers will answer, but if a greater length of bridge is required it may be supported on piles or trestles, or in deep water on rafts of logs or casks. But the heavy traffic of armies, operating at some distance from their bases, must be transported by rail, and the building of railway bridges or rebuilding those destroyed by the enemy is an important duty of the engineer. On the Potomac Creek, in Virginia, a trestle bridge 80 feet high and 400 feet long was built in nine working days, from timber out of the neighborhood. Another bridge across the Etowah River, in Georgia, was built in Gen. Sherman's campaign, and a similar bridge was also built over the Chattahoochee.

SURVEYS AND EXPLORATIONS.

For more than half a century before the building of the great Pacific railways, engineer officers were engaged in making surveys and explorations in the great unknown country west of the Mississippi River, and the final map of that country was literally covered with a network of trails made by them. Several of these officers lost their lives in such expeditions, while others lived to become more famous as commanders during the great rebellion. Generals Kearney, J.E. Johnston, Pope, Warren, Fremont and Parke, and Colonels Long, Bache, Emory, Whipple, Woodruff and Simpson, Captains Warner, Stansbury, Gunnison and many other officers, generally in their younger days, contributed their quota to the geographical knowledge of the country, and made possible the wonderful network of railways guarded by military posts that has followed their footsteps. Their reports fill twelve large quarto volumes.

BOUNDARY AND LAKE SURVEYS.

The astronomical location of the boundaries of the several States and Territories, as well as of the United States, is a duty frequently required of the engineer officer, and such a survey between this country and Mexico is now in progress. The entire line of the 49th parallel of latitude from the Lake of the Woods to the Pacific Ocean, which forms our northern boundary, was located a few years ago by a joint commission of English and United States engineers, and monuments were established at short intervals over its entire length.

A careful geodetic and hydrographic survey of the Great Northern Lakes, including every harbor upon them and the rivers connecting them, was carried on for many years and was finally completed some ten years ago. Maps and charts of these surveys are published from time to time for use of pilots navigating these waters.

Not only are the duties of the military engineer similar in many respects to those of the civil engineer, but there are many instances in which the duties of one branch of the profession have been performed by members of the other branch, quite as efficiently as though they had been performed by engineers specially educated for the purpose. During the late civil war there were many illustrations of this, all showing that an ingenious engineer can readily adapt himself to circumstances entirely different from those to which he has been accustomed. A very good example of this occurred in the Red River expedition of General Banks and Admiral Porter. In that memorable but disastrous campaign an army accompanied by a fleet of transports and light draught gunboats, sometimes called "tin clads" because some parts of them were covered with boiler plate to stop the bullets of the enemy, ascended the Red River in Louisiana; but the advance having been checked and a retreat commenced, it was found that the river had fallen to such a low state that the fleet was caught above the rapids near Alexandria, and it would in all probability have been a complete loss had it not been for the timely application of engineering skill by Lieut. Col. Joseph Bailey, a civil engineer from Wisconsin, who built a temporary dam across the river below the rapids and floated out the entire fleet. This dam was over 750 feet long and in connection with some auxiliary dams raised the water level some 6½ feet. It was built under many difficulties, but by the skill and ability of the engineer and the co-operation of the troops it was completed in ten days. Another case was at the siege of Petersburg, Va., where Lieut. Col. Pleasants, a Pennsylvania coal miner, ran a gallery from our lines, under the rebel battery, some 500 feet distant, and blew it entirely out of existence. The mine contained four tons of powder and produced a crater 200 feet by 50 feet and 25 feet deep, and was completed in one month. The sequel to this was to be an attack on the enemy's line through the gap made by the explosion, and such an attack properly followed up would doubtless have had a marked effect in shortening the duration of the war, but this attack was so badly managed that it utterly failed and caused a severe loss to our own army. The mine itself, however, was a great success and produced a decided moral effect on both sides which lasted until the end of the war.