DEFENSES OF THE COLUMBIA-continued. The works command the channels at the entrance, the ship-channels leading to Astoria, and the anchorage in Baker's Bay under the lee of the cape on the north. The channels to the river have natural depths of 19 to 24 feet at low water, and a mean rise of tide above this plane of 71⁄2 feet. These defenses are field works in character; they were built hastily during the late civil war in anticipation of complications with foreign powers. On account of increased penetration of present ordnance, and and the decay of the greater part of the wooden platforms and magazine timbers, the works are of little value in their present condition except for drill purposes. Fort Stevens, Oregon.-During August and September the marsh sod revetment of the interior slope was repaired; four shot-platforms and five gun-platforms were constructed in place of decayed ones; in June the magazine was wholly rebuilt, except replacing part of the earth covering. Fort Canby, Washington.—The service magazine and three gun platforms at the center battery were rebuilt, placing this battery in good condition throughout; minor repairs were made to the right battery magazine, and timber received for rebuilding magazine at left battery. Many of the platforms of the batteries are in an unserviceable condition. No appropriation was made for the fiscal year ending June 30, 1885. BOARDS OF ENGINEERS. 4 THE BOARD OF ENGINEERS. The Board of Engineers stationed in New York City consisted of Col. John Newton (until March 6, 1884), Col. J. C. Duane (since April 12, 1884), Lieut. Col. Heury L. Abbot, Lieut. Col. Cyrus B. Comstock, and, when so ordered, the officer in charge of the work under consideration. The Board has been engaged in the duties which have from time to time been referred to it, and has submitted the following report of its operations: Coast defenses.-The defenseless condition of our sea-coast and the urgent necessity that immediate steps be taken to remedy this evil have been so frequently and thoroughly discussed that further remarks on this subject are unnecessary. Any one who has taken the trouble to investigate the matter must be aware that our harbor defenses, which were all constructed many years since, and were designed to contend with wooden ships armed with smooth-bore guns of moderate dimensions, are utterly unable to cope with an iron-clad fleet armed with the modern rifled gun, and that in fact such a fleet could destroy our torpedo defenses, run past our batteries, and enter any harbor in this country with perfect impunity. Any system of defense which will effectually avert such a disaster will necessarily involve the employment of both batteries and obstructions. Neither guns nor mines alone can stop a fleet. Without the latter, ships can run by any battery, either by taking advantage of the night or a fog, or, if well protected by armor, can even do so in broad daylight. On the other hand, if the mines are unprotected, their detruction by the enemy is a mere question of time. The first requisite for defense is therefore the thorough obstruction of the channels by mines and the protection of the mines by batteries especially designed for the purpose. Next in order will be the establishment of batteries armed with guns at least equal in power and as well protected as those carried on ships of war. Under present conditions this will require 100-ton rifles mounted in revolving iron turrets. This method of mounting guns is without doubt the most perfect that has yet been devised. Nevertheless, the great cost of construction and the necessity for using steam-power for working the turrets will limit their employment to the protection of guns of the heaviest caliber, such as the 100-ton rifle. The method of mounting guns of inferior caliber will depend on circumstances. The modern naval vessel, in addition to its heavy batteries, is liberally supplied with small rifled guns, howitzers, and Hotchkiss or other machine guns. If the defensive battery is so located as to be exposed to a concentrated fire of this description, the guns must either be mounted on disappearing carriages or be protected by iron armor. In the former case the guns will have a considerable horizontal range, but must be worked by steam-power. In the latter the horizontal range is restricted, but the gun is much better protected and can be worked by hand. The rifled mortar has lately been so much improved, both as regards accuracy of fire and weight and range of its projectile, that it is destined to play a very important part in sea coast defense. It is true that its fire is less accurate than that of the rifled gun firing at low angles; nevertheless, as it can be completely covered from the enemy's missiles of every description, the effect of its enormous projectile falling vertically on the deck of a vessel must be so disastrous that a fleet could not hold any position exposed to the fire of two or three groups of 12inch rifled sea coast mortars. Without doubt harbors can be effectually defended by the means above described. But in order to carry out such a design heavy steel rifled guns are required, and from present indications it will be many years before such guns are made in this country. We have, however, certain seaports whose safety is of such vital importance to the whole country that any delay in thoroughly protecting them is inadmissible. For such points guns and armor must be imported. There is one part of this defensive project that can and should be commenced without further delay. All the material required for obstructing the channels leading to our principal harbors should be procured and stored ready for use. The operating-rooms and galleries leading from them to the mines should be built, and should be so constructed as to be absolutely secure from attack, both by bombardment and assault. The batteries for the protection of the mines should be built and armed. There will be no difficulty in procuring the armament, as these batteries are designed to drive off the small craft sent out from the attacking fleet to destroy the mines and tear up the cables. The guns required will be of moderate size, with an ample allowance of Hotchkiss and other machine guns, and their arrangement must be such that, while their fire thoroughly sweeps the entire emplacement of the mines, they cannot be silenced by the fire from the attacking fleet. Finally, the position must be defended by a work secure from assault, and having ample bomb-proof shelter for all the force required to operate and defend the mines. This method of channel obstruction is applicable to the defense of all harbors. The selection and disposition of the guns in the batteries destined to receive and return the fire from the attacking fleet will be determined by local circumstances. If the water is so shoal as to permit the approach of light-draught vessels only, barbette batteries may suffice. Where the channel is deep, but so narrow as to compel the ships to move up in single file and attack bow on, heavy guns should be mounted in iron casemates, supported by batteries of lighter guns mounted in barbette; but when the channel is both broad and deep, with ample room for the development of the attack, every available means of defense must be employed. As an example take the southern entrance to New York Harbor. Having thoroughly obstructed the channel in the vicinity of the Narrows, there will be required on the site of Fort Lafayette two revolving iron turrets, each armed with two 100-ton guns; in the vicinity of Fort Hamilton an iron casemated battery mounting ten 50-ton guns, supported by batteries of ten 20 or 30-ton guns, mounted on disappearing carriages and protected by earthen parapets; and in the same vicinity a battery of forty-eight 12-inch rifled mortars. On the Staten Island side of the Narrows a similar provision of turrets, iron casemates, barbette, and mortar batteries. With this protection it is not probable that any fleet would attempt to force its way through the Narrows. RECAPITULATION AND ESTIMATES. To recapitulate, the elements of defense for the entrance to a harbor are: 1. Lines of submarine mines or other obstructions to detain the enemy's vessels under fire. 2. A defense of these obstructions against an attack of unarmored vessels or of launches and boats, which can be effected by covered guns of moderate power aided by armed launches. 3. A defense which shall make it impossible for armored vessels to close on the mines and silence the flanking defense, when their removal would be a simple matter. This last part of the defense is the most difficult, the most costly, and the most important, as it alone protects itself. It will only be sufficient. when it employs guns equal in number, equal in power, and as well protected as those which the attacking fleets can bring against the works. With these considerations in view, the Board submits approximate estimates of cost of heavy guns and emplacements needed for some of our more important harbors. With the torpedo defense, which is relatively cheap, they would give a fairly good defense for these cities. The Board cannot state too emphatically that, if the money were now available, three years would be required to provide either the guns or the forts necessary for New York Harbor alone, if we were to go at once to the great private gun and armor establishments of England, Germany, and France. If they were to be obtained in this country a much longer time would be needed. It seems scarcely necessary to say that no naval power which may see fit to attack our seaports is likely to warn us of it three years, two years, or one year in advance. Considering the great increase in power of rifled guns, the estimated penetration in iron of the new 110-ton Elswick gun being at 1,000 yards 30 inches, the Board deems it advisable to make the armor of turrets or casemates not less than 36 inches thick if of wrought iron, or oi equivalent resistance if of other material. In view of the rapid improvements recently made in guns, the best of the modern types should be selected. The estimates are for steel guns, and the prices approximately those of Krupp, the largest manufacturer of guns in the world. The following are the estimates for heavy guns and emplacements needed for New York, Philadelphia, Boston, and Baltimore. If the cost of torpedoes and their flanking defenses, of modification of existing works and of sites, be added, the sums given below for each work would be increased about 25 per cent. NEW YORK. NARROWS. Four 2-gun turrets at Narrows, at $600,000 Twenty 50-ton breech-loading rifles, at $50,000 $2,400,000 800,000 2,000,000 1,000,000 600,000 400,000 1,632, 000 8,832,000 EAST RIVER.-WILLETS POINT AND FORT SCHUYLER. Three 2-gun turrets, at $600,000 Six 100-ton breech-loading rifles, at $100,000. Ten 50-ton breech-loading rifles, at $50,000 Ten emplacements for barbette disappearing rifles, at $30,000. PHILADELPHIA. AT PEA PATCH ISLAND. Ten iron casemates, at $100,000 BOSTON. Ten 50-ton breech-loading rifles, at $50,000.. Fifteen emplacements for barbette disappearing rifles, at $30,000. Ten barbette breech-loading rifles, not elevating, including emplacements, at $25,000... One hundred 12-inch rifled mortars and emplacements, at $17,000.. BALTIMORE. AT FORT CARROLL AND HAWKINS' POINT. Five iron casemates, at $100,000. Five 50-ton breech-loading rifles, at $50,000.... $500,000 Ten emplacements for barbette, disappearing rifles, at $30,000 250,000 300,000 200,000 272,000 1,522,000 Torpedo defense-The appropriation of $75,000, to be expended during the fiscal year 1883-'84 for providing materials to defend our coast with submarine mines, &c., was chiefly allotted, on the recommendation of this Board, to the purchase of torpedo-cases for obstructing approaches to the bay of San Francisco (about $50,000), to purchasing two Sims fish torpedoes, complete except the motors ($17,000), and to continuing the investigations to perfect this torpedo for the requirements of our service. The investigations for perfecting our system of defensive submarine mining have been continued, as heretofore, at Willets Point by, General Abbot, from whose report the following extracts are made: In the matter of new explosives considerable progress has been made. After much difficulty and delay a ton of explosive gelatine (without camphor) has been received from Nobel's Explosive Company, limited, of Glasgow; and the experiments to compare it with the camphorated sample of home manufacture, formerly tested, and to accurately determine its fitness for the torpedo service, are now in progress. They already indicate that in explosive intensity of action under water the uncamphorated material is decidedly the stronger, and indeed is the strongest explosive ever tested at Willets Point. At the request of the Chief of Ordnance a sample was transferred to that department for trial in shell-firing from cannon at the proving ground at Sandy Hook. Ring trials have been completed with two grades of Atlas powder, and are now in progress with two grades of Judson powder and an improved quality of Rackarock, to test their relative merits in subaqueous work. Forty-three explosions have been already measured, and it is expected to complete the tests of these powders, and perhaps of another new variety, during the present season. The general results with Atlas powder are the following: It is manufactured by the Repauno Chemical Company, at Gibbstown, N. J. Grade A is reported to contain 75 per cent. of nitro-glycerine and 25 per cent. of a compound base mostly composed of wood fiber. Grade B is reported to contain 50 per cent. of nitro-glycerine and 50 per cent. of an explosive base chiefly composed of nitrate of soda and wood fiber. Fourteen shots (giving eighty-four gauge records) were fired in the rings with each variety, and the analysis indicates that grade A is precisely equal to dynamite No. 1 in explosive intensity of action when fired under water, and that grade B has 99 per cent. of the same strength under the same conditions. The small difference between the two grades is surprising, considering the different chemical compositions, and it can only be affirmed for subaqueous explosions. There is considerable difference in price between the two grades, and the powder is worthy of the attention of officers of the corps directing blasting operations. At the electrical exhibition at Vienna, in 1883, the Danish submarine mining service exhibited a platinum wire fuze of extraordinary sensitiveness, far exceeding any made before that date. A novel system of operating mines not without promise of practical value, was based upon this peculiarity, and it appeared important for us to turn our attention in this direction. Samples of the Danish fuzes or of their wire could not be procured; but I have finally succeeded in making from materials obtained in this country fuzes considerably more sensitive than those exhibited at Vienna. The Danish fuzes were thus reported: Diameter of bridge-wire, in millimeters, 0.0005 to 0.000675; length of bridge-wire, 11 millimeters, of which 2 millimeters have the above fine gauge; resistance 9 to 14 ohms; firing current, 0.38 to 0.05 ampéres. |