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THE MORTAR FLEET OF COMMANDER PORTER.
This fleet left New York some time since for the South, but its exact destination has not yet been made known. It has a most formidable mortar armament, and much curiosity is felt to ascertain what particular point in the South it will strike at. The plans for the expedition were formed several months since, but it has taken some time to make preparations, and especially for the elaborate experiments which have been instituted in order to test the strength of the heavy mortars with which the fleet is armed. It was fitted out at the Brooklyn Navy Yard. As much interest has been expressed in the objects of the expedition, and in the manner in which it has been organized, we have compiled from a New York paper the following interesting facts, which are worthy of being placed on record :
The twenty heavy mortars which form the Principal armament of the fleet were cast at ittsburg, and are of immense size and strength. Their average weight is over seventeen thousand pounds, or eight and a half — almost equal to the weight ofthe ten-inch columbiads, which are nearly three times the length of the mortars. The diameter of the bore is thirteen inches. The total depth of the bore is thirty-five inches, a little more than two and a half times its diameter. But the most remarkable feature in their construction is the thickness of metal around the bore, which is at every point no less than fifteen inches. The trunnions measure fifteen inches in diameter. The entire length of the mortar is fifty inches, and the aggregate diameter forty-three inches, or more than three and a half feet.
Ordinary mortars are quite light compared with their caliber. Those of English manufacture, of thirteen-inch bore, weigh from two tons (laud service) to five tons and a fraction (the heaviest seacoast mortars). Those with which Commodore Porter's vessels are provided — which may be used alike for sea and land service — are about double the weight and strength ofthe "approved" English mortars, which have frequently burst, though comparatively small charges of powder were used and short ranges obtained.
Commander Porter's mortars are elevated or depressed by means of cog-like projections on the breech, into which a fever fits, supported by the framework of the carriage. By means of the accurate working ofthe revolving platform and the carriage, ranges can easily be obtained. It is believed that accurate firing may be made at a distance of two and a quarter miles. The vessels ofthe mortar fleet number twentyone, and, with the exception of the flag-ship, are sailing vessels. Nearly all of these are schooners of two or three hundred tons burthen. Originally they were fitted out as war vessels, and pierced for four or six guns. Steamers cannot be advantageously employed, the ponderous mortars necessarily occupying the center of the vessel, so that the position usually assigned to the engines or machinery of a steamer is taken up. Besides, these small vessels are stronger in proportion than large ones ; their light draft fitting them for the navigation of shallow waters, and their small tonnage requiring comparatively few men to manage them. Moreover, as a mortar vessel fights best at anchor, facility of movement is unnecessary. , The adaptation of these schooners to the mortars'* service is admirable. An almost solid mass of wood has been built from the keel to the upper deck. This staunch groundwork is composed of timbers over one foot square and twelve feet in length, interlaced and firmly, fastened. Ttvo or three inches above the upper deck the V bed " is built, consisting of a solid horizontal surface, circular in form, with a "track" near its edge, upon which run rollers bearing a revolving platform. The great mortar bed is carefully braced and supported by the entire strength of the vessel, so as to bear the recoil of the mortar. The design is apparently perfect.
The circular platform surmounting the bed and bearing the mortar carriage, is constructed of heavy timbers, and is one foot in depth and nearly twelve feet in diameter. When in position for a discharge it lies flat and firmly on the bed, but by ingenious mechanism it may be made to revolve, in order to aim the mortar in any direction, or to resight it if the vessel shifts its position. The change of direction is easily and quickly accomplished. By means of four eccentric axles in the platform, to which levers are fitted, the mortar and machinery (weighing altogether over ten tons) may be raised, and the weight transferred by the same movement to a great number of metallic rollers attached to a framework of immense strength under the platform. Then by means of tackle, already arranged, the whole mass may be moved to its desired position, and instantly, by a reverse movement, replaced on the bed. In the center of the platform, and extending into the solid mass beneath, is an iron cylinder or spindle which prevents any side movement. Tne arrangement of this machinery is very simple, and the invention is . attributed to one of the Lieutenants of the Navy. The mortar carriage is constructed almost exclusively of wrought iron. Its length is about nine feet, and its bight and width each four feet. In form it bears the slightest possible resemblance to a land carriage — gradually sloping at the point where the mortar rests, in the direction of the breech ; and having wheels, yet not resting on them when the mortar is discharged. The carriage is composed principally of plate iron, riveted together, braced and bolted. It is a framework of excellent design, and, though weighing probably, not more than two tons, is capable of resisting a pressure . of one to two hundred tons.
Two wheels are set close to the framework, directly under the mortars and connected with them are eccentric axles, so arranged as to per-
mil so large a part of the weight to be thrown on the wheels, that the carriage may be moved on them. _
It is not intended, hawever, that the recoil of J the mortar shall in any de_rree be taken up or lessened ** in its effect by the . moving of the wheels.' The I carriage Ties firmly -on the platform when . the mortar is discharged, and the only possible motion will be that of the vessel in the water. The bombshells to be thrown from the mortars are of the ordinary description, resembling round shot, but hollow, and weighing unfilled over two hundred pounds each, the most formidable ordnance missiles known in modern warfare, with the single exception of those used iv the Rodman columbiad, of fifteen inch bore. Between seven and eight thousand of these bombs have been furnished for the flotilla, and it is understood that the amount of explosive material contained in each shell exceeds twelve hundred pounds; the powder having been carefully granulated expressly for this purpose. In addition to the mortar armament, each vessel of the fleet has been provided with t .vo "long thirty-two's," of the best description of smooth-bore ordnance. Each of these weighs thirty-seven hundred weight, and throws round shot and shell.' The vessels are also provided with swords, pikes and other necessary weapons. The entire fitting out, with the exception of the mortars, is quite similar to that of ordid in. iry war vessels. Partial instructions, including a record of the results of the mortar experiments so far made by the Ordnance Bureau, have been transmitted to the flotilla; but they are accompanied by the statement that the Department will find in the result of the expedition the material most needed for perfecting the instructions, and a thorough understanding of the subject. It is understood that a code of signals has been adopted, and the method of placing and anchoring the vessels for attack determined upon. The mortars cannot safely be fired directly over the sides of the vessels, and therefore the fleet must be partially headed towards the point of attack, which is, however, a better position in respect to the enemy's guns, than with the broadside exposed. The officers are ordered to anchor in a proper position, and to remove a part of the rigging of the vessels, and to trust to their best judgment in the necessary absence of explicit instructions. The effect of the firing cannot at present be accurately estimated. The extraordinary weight and strength of the mortars; the charge of powder (unprecedently large in mortar practice), the long range and high velocity of the projectiles, and their terribly destructive character, combine to render the expedition one of the most important that has been undertaken during the war.
The fleet will be arranged in three divisions, as follows :
Flag Ship— Side-wheel gunboat Octorora, Commander D. 1). Porter, commanding. First Division— (Lieutenant Watson Smith commanding) — Schooners Norfolk Packet, (flag vessel), Oliver Lee, Win. Bacon, Arietta, C. P. Williams, Para. Second Division (Lieutenant W. W. Queen commanding) — T. A. Ward (flag vessel), George Mangun, AdolphusHugel, Matthew Vassar, Jr., Sydney C. Jones, Maria J. Carlton, Orvetta.
Third Division (Lieutenant R. Randolph Breese commanding) — Schooners .1. Griffith, (flag vessel), Racer, Sarah Bruen, Sea Foam, (brig rigged , Henry Jones, Dan Smith. The Horace Beale and A. Houghton are also of the flotilla. It is understood they will carry on!}- ordnance and ordnance stores and subsistence.