1841. He utilized it by enclosing a tube of cast-iron or steel in

the same manner as it is applied in the wrought-iron Armstrong and Woolwich guns. [Illustration: PUTTING THE JACKET ON A 6-INCH BREECH-LOADING RIFLE-TUBE.] The administration of our naval ordnance has abandoned conversions, and has concentrated its efforts on the production of an armament of built-up steel guns. The system of construction that has been adopted originated in England, but was for many years ignored by the government authorities. It involved the use of steel in all its parts, and this was charged as an objection, as confidence in this metal was not established in the minds of the English artillerists. That government committed itself entirely to the wrought-iron gun proposed by Mr. (now Lord) Armstrong, whose system was a reproduction of that successfully experimented on by Professor Treadwell, and the entire force of the government works at Woolwich and of the Armstrong works at Elswick-on-the-Tyne was occupied with the production of this style of ordnance. The English steel gun invented by Captain Blakely and Mr. J. Vavasseur was ignored in England, but its merit could not be suppressed, and its superiority has forced a tardy recognition by that government. This gun came prominently into notice for a short time at the breaking out of the war of the rebellion: some guns were imported for the service of the Southern States. At the exhibition in London in 1862 a Blakely 8.5-inch gun was one of the features of attraction in the department of ordnance. The principle of the construction was shown in this gun, consisting in shrinking a long jacket of steel around an enclosed steel tube, the jacket extending to the trunnions. Mr. Vavasseur was the manager of the London Ordnance Works, and was associated with Captain Blakely in the manufacture of his earlier guns, but the entire business soon fell into the hands of Mr. Vavasseur, whose name alone is associated with the succeeding developments of the gun. In 1862 the guns manufactured by Mr. Krupp were solid forgings. He advanced but slowly towards the construction of built-up cannons, and it was not until the failure of some of his solid-cast guns that he entered on the built-up system. His first steps were to strengthen the rear portion of new guns by shrinking on hoops, and to increase the strength of old guns he turned down the breech and shrunk on hoops. He confined this system of strengthening to the rear of the trunnions until he was reminded of the necessity of strength along the chase of the gun by the blowing off of the chase of some 11-inch guns of his manufacture. His system was then modified so as to involve reinforcing the tube of the larger calibred guns along its whole length with hoops, and his later and largest productions are provided with a long jacket reinforcing the entire breech portion of the tube—a virtual adoption of the great element of strength which has always formed the essential feature in the Vavasseur gun which is now adopted in the United States navy. In the building up of the steel gun for the navy advantage is so taken of the elastic characteristic of the metal that all parts tend to mutual support. The gun proper consists of a steel tube and a steel jacket shrunk around it, reaching from the breech to and beyond the location of the trunnion-band. Outside the jacket and along the chase of the gun there are shrunk on such hoops as the known strain on the tube may make necessary for its support. The tube is formed from a casting which is forged, rough-bored, and turned, and then tempered in oil, by which its elasticity and tensile strength are much increased. It is then turned on the exterior, and adjusted to the jacket, the proper difference being allowed for shrinkage. The jacket, previously turned and tempered, is then heated, and rapidly lowered to its place. The front hoops over the chase are then put on, and the gun is put into a lathe and turned to receive the trunnion-band and rear and front hoops. The gun is then fine-bored and rifled. [Illustration: BREECH-LOADING RIFLE AFTER RECEIVING JACKET.] Each part, as successively placed in position, is expected to compress the parts enclosed through the initial tension due to contraction in cooling. This tension is the greater the farther the part is removed from the tube; thus the jacket is shrunk on at a less tension than are the encircling hoops. By this means full use is made of the elastic capacity of the tube which contributes the first resistance to the expanding influence of the charge. The tension of the jacket prevents the tube being forced up to its elastic limit, and it in turn experiences the effect of the tension of the other encircling parts which contribute to the general support; thus no part is strained beyond its elastic limit, and on the cessation of the pressure all resume their normal form and dimensions. A comparison of this method of common and mutual support of parts with that given by the wall of a gun cast solid will serve to demonstrate the superior strength of the construction. In order to achieve this intimate working of all the parts it is necessary that the metal of which they are respectively composed must be possessed of the same essential characteristics; in a word, the gun must be homogeneous. It was the absence of this feature in the Armstrong gun which has caused its abolition. This gun was built up, and the parts were expected to contribute mutual support, but the want of homogeneity between the steel tube and the encircling hoops of wrought-iron made it impossible for them to work in accord, in consequence of the different elastic properties of the two metals, which, after frequent discharges, resulted in a separation of surfaces between the tube and hoops, when the tube cracked from want of support. [Illustration: A KRUPP HAMMER.] [Illustration: TRANSPORTING CANNON AT BREMERHAVEN.] In the construction of the guns for the United States navy, as in the new steel guns now being manufactured in England, the theory of the built-up system is practically conformed to; more so than by Krupp or the French artillerists, who use a thicker tube than is considered judicious at Woolwich or at the Washington navy-yard. Any increase of thickness of the tube beyond what is necessary to receive the initial pressure of the charge is open to the objections made to the gun with a solid wall, the proportion of the strain communicated to the hoops is reduced, and rupture may ensue from overstraining the tube. The thicker the tube, the less appreciable must be the compression induced by the tension of the encircling hoops. [Illustration: BREECH-LOADING RIFLE AFTER RECEIVING JACKET AND CHASE HOOPS.] [Illustration: BREECH-LOADING RIFLE WITH JACKET, CHASE HOOPS, AND JACKET HOOPS IN PLACE.] The gun is a breech-loader. The system adopted for closing the breech is an American invention (see note, p. 257), but having been employed in France from the earliest experimental period, it is known as the French _fermeture_. A screw is cut in the rear end of the jacket to the rear of the tube, and a corresponding screw is cut upon a breech-plug. The screw threads are stripped at three equidistant places, the screw and plane surfaces alternating, thus forming what is called an “interrupted” or “slotted” screw. The screw portions of the breech-plug enter freely along the plane longitudinal surfaces cut in the tube, and being then turned one-sixth of its circumference, the screw of the plug locks in that of the tube, and the breech is closed. [Illustration: U.S.N. 6-INCH BREECH-LOADING RIFLE.] The success of this system of breech mechanism was not so pronounced on its introduction as it is to-day. The plug forms the base of the breech of the gun, and all the effort of the gases to blow out the breech is exerted at this point. The impact upon the end of the plug is very severe, and has a tendency to _upset_ the metal, thereby increasing the diameter of the plug, which would prevent its removal after the discharge of the piece. With quick-burning powder, as was generally in use for cannons at the inception of the breech-loading experiments, this result ensued if the charges of powder were carried above a certain limit, and the consequent restriction that was put upon velocities was a serious obstacle to the adoption of the system; but the progress that has been made of late years in the science of gunpowder manufacture has relieved the subject from this embarrassment, powder being now provided which communicates very high velocities while developing pressures so moderate and regular as to be entirely under the control of the artillerist. The original guns, four in number, constructed with breech mechanism on the French _fermeture_ principle for the British government during the Crimean war are now in the “Graveyard” at Woolwich Arsenal. The projectiles for the new armament are of two kinds; both, however, are shells. That for ordinary use against unarmored vessels is styled the common shell, and is of cast-iron. The length bears a uniform proportion to the gun, being in all cases three and a half calibres. The armor-piercing shell is made of forged steel, and is three calibres in length. The following table gives the particulars, approximately, of the common shell: +------------------------------+------------------+--------+---------+ | GUN. | Length. | Weight.| Bursting| | | | | Charge. | +------------------------------+--------+---------+--------+---------+ | | Inches.| Calibre.| Pounds.| Pounds. | | 5 inch breech-loading rifle | 17.97 | 3.59 | 60 | 2 | | 6-inch breech-loading rifle | 20.90 | 3.48 | 100 | 4 | | 8-inch breech-loading rifle | 28.10 | 3.51 | 250 | 12 | | 10 inch breech-loading rifle | 35.00 | 3.50 | 500 | 22 | | 12 inch breech-loading rifle | 42.00 | 3.50 | 850 | 38 | | 16-inch breech-loading rifle | 56.00 | 3.50 | 2000 | 90 | +------------------------------+--------+---------+--------+---------+ The armor-piercing shell of the same weight is reduced in length, and its walls are thicker; the bursting charge is consequently much reduced. The following are the particulars, approximately determined: +------------------------------+------------------+--------+---------+ | GUN. | Length. | Weight.| Bursting| | | | | Charge. | +------------------------------+--------+---------+--------+---------+ | | Inches.| Calibre.| Pounds.| Pounds. | | 5-inch breech-loading rifle | 15.07 | 3.01 | 60 | 1 | | 6-inch breech-loading rifle | 17.91 | 2.98 | 100 | 1.50 | | 8-inch breech-loading rifle | 24.25 | 3.03 | 250 | 3.50 | | 10-inch breech-loading rifle | 30.00 | 3.00 | 500 | 7 | | 12-inch breech-loading rifle | 36.00 | 3.00 | 850 | 14 | | 16-inch breech-loading rifle | 48.00 | 3.00 | 2000 | 30 | +------------------------------+--------+---------+--------+---------+ The rifle motion is communicated by one rotating ring of copper, which is placed at the distance of 1.5 inch from the base of the projectile. [Illustration: CARTRIDGE CASE AND GRAINS OF POWDER, U.S.N.] The uniform windage for all calibres is .04 inch; thus, taking the 6-inch gun as an example, the diameter of the bore across the lands is 6 inches, the diameter of the shell is 5.96 inches, the depth of the grooves is .05 inch; thus the diameter of the bore across the grooves is 6.10 inches. In order to permit the rotating ring to fill the grooves, it must have a diameter of 6.14 inches; this causes a _squeeze_ of .05 inch between the lands and the rotating ring. There is no subject in the development of the new naval artillery more important than the powder. That used with the old artillery is entirely unsuited to the new conditions that obtain in the modern high-power guns. A brown powder, introduced first in Germany, has exhibited decided advantages over all others, and the efforts to reproduce it have been thoroughly successful at the Du Pont Mills. It is generally known as “cocoa” powder. Its peculiarity exists in the method of preparing the charcoal; this affects the color, and results in a brown instead of a black powder. With this powder, experiments with the 6-inch gun give a muzzle velocity of over 2000 feet per second with a projectile of 100 pounds, using charges of 50 pounds, and this result is obtained with less than 15 tons pressure per square inch in the powder chamber. The grain is prismatic, with a central perforation, and as regards its rate of burning, is under complete control in the manufacture; the form provides an increasing surface for the flame during the period of combustion, thus relieving the gun from abnormal pressures at the moment of ignition, but continuing the extreme pressure farther along the bore. The progressive nature of the combustion is very apparent when comparing an unburned grain with others partially consumed, blown out from the gun. [Illustration: COMMON SHELLS, U.S.N.] The gun-carriage, which is a separate study in itself, is carried to a high pitch of perfection, and presents many features being adopted abroad. The importance of a suitable carriage can be appreciated by inspecting the following table, which exhibits the _energy_ that must be controlled by it: