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.