The increased powder charges and pressures in rifled guns — especially the breech-loaders and in smooth-bore guns which attempted to compete with them led to strains which ordi nary cast-iron guns were unable to withstand. Rodman introduced improved methods of cast ing and a slower burning powder, but the real solution was found to be in built up guns— first of wrought iron or cast-steel and eventu ally of forged steel. The stresses upon the various layers of metal about thelore of a gun are nearly in. proportion to the square of the distance of the layer from the axis of the bore. The outer part of a thick homogeneous tube would therefore be but slightly affected when the inner part would be strained beyond the breaking point. Layers of varying strength and elasticity were therefore necessary. Further strength was given by shrinking the outer tubes, jackets, and hoops upon the inner ones. This placed the latter in a state of initial com pression so that they were not strained at all until considerable stress was felt by the outer layers. Wire-winding of guns was suggested by Dr. Woodbridge, an American ordnance engi neer, in the early days of built-up guns but the principle was not developed to a practical solution for many decades. The cast-iron smooth-bore shell gun reached the culmination of its development during the Civil War under conditions which rendered its use not unduly inefficient compared with the rifle. And it was retained in the American navy for nearly 20 years after it was obsolete because of the parsimony of Congress in naval and military affairs combined with undue admiration for its performances in the war. The next step in gun development after the adoption of rifling was the increase of velocity due to im proved powder. The combustion of the powder in common use was so rapid that the gas pres sure in the gun reached its maximum before the projectile started to move and then fell so quickly as to be almost negligible, so far as propulsive effort was concerned, when the shell reached the muzzle. About 1856, Major Rod man of the United States Army developed his system of making slow-burning gunpowder by which the maximum pressure was kept within bounds while the average pressure was consid erably augmented. But the black powder of that day could only be controlled within narrow limits. About 1880, a slower burning powder made from incompletely charred wood came into use. From its color it was known as brown or cocoa powder. It ignited readily but burned slowly so that with a given maximum pressure the sustained pressure was much great er. To efficiently use the new powder longer guns were necessary and the length jumped from about 20 to 30 and 35 calibres.
In 1881 was initiated a movement which led to most important changes in the construction of the breech mechanism of guns and the means and methods of loading. Up to this time no great effort had been made to accelerate the speed of loading and the time wasted, even in operating small pieces, was absurd. Toward the end of 1881 the British Admiralty adver tised for designs of a gun that should fulfill the following requirements: weight of gun and mount not to exceed 10 hundredweight (1,120 pounds) ; projectile to weigh 6 pounds and have a muzzle velocity of at least 1,800 feet per second; projectile and powder to be made up in one cartridge; service of the gun to require not more than three men; under the foregoing conditions the gun to be capable of firing at least 12 aimed shots per minute. About the same time the French Minister of Marine invited proposals for a 3-pounder gun which was required to fulfill the same relative conditions. In answer to these proposals the first guns were produced. Mr. B. B. Hotchkiss, an American ordnance engineer and manufacturer who had established an ordnance factory in Paris about 1870, brought out a series of guns — one, three, and six pounders. While his guns were accepted by nearly all foreign navies, his first order was from the United States navy which had just laid down the first ships of its modern fleet. Mr. Nordenfeldt brought out very similar guns in England. The six and three pounder guns called for by the British and French navies were intended for use against torpedo boats which were then small and weak. The success of these guns led to an extension of the principle to larger cali bres, but it was some years before the breech mechanisms of guns larger than the 4-inch were satisfactory. Every form of breech clo
sure in which the operation had been acceler ated was styled by its makers, but in 1887. Numerous other types appeared al most at once, a large proportion of which con tained nitroglycerin as the principal ingredient. The erosive effect of the nitroglycerin powders caused such rapid destruction of the rifling that the proportion of nitroglycerin was stead ily reduced, until most modern powders contain only a small percentage of it or are made solely from guncotton. As the manufacture of smokeless powder progressed, guns were ex tended until a length of 50 calibres was reached in large pieces and 60 or even 80 in small ones. The limit was not due to the inability to con trol the rate of combustion of the powder but to the fact that in a length of more than 50 calibres adequate stiffness or rigidity of the gun entails a weight that can be more profit ably employed in a gun of larger calibre and less relative length (s. e., expressed in calibres of the bore).
In the decade of 1890-1900 much attention was paid to the question of strengthening guns by winding them with steel-wire of very high grade. The process was brought to reasonable perfection by using wire of ribbon form or of some special section laid on with the proper increasing tension. Guns which are wire the term was finally restricted to guns in which the breech was opened by the simple throw of a lever. At first, the charge and projectile were made up in a single cartridge but in cali bres above 5-inch this was found impracticable and after 1897 the charges for guns of calibres exceeding 5-inch were as a rule not even cased. While the breech-mechanism of guns of 8-inch calibre and over was not adapted to easy opera tion by a simple hand lever, the speed of open ing and closing the breech and of loading was relatively as much increased as in small guns. In 1884 the average time required to load a 12-inch gun was four minutes; in 1914, for naval guns it was not more than 20 seconds.
The automatic principle which is so success ful in machine guns has been applied to pieces of greater calibre but without success in those larger than the one-pounder. Semi-automatic guns of three-inch calibre are, however, now common. In these the force of recoil is util ized to open the breech and eject the empty cartridge case, the closing of the breech being effected by inserting the cartridge smartly so that it trips a pawl on the breech-plug which is then closed by a spring compressed during recoil. The next step in augmenting the power f o guns' was due to the production of smoke less gunpowder. Its smokeless feature is highly desirable, but an equally or more im portant gain is the facility by which the rate of combustion can be controlled. Between 1865 and 1870, Schultze in Germany and Von Lenk in Austria developed smokeless powders from nitrated cellulose, but they were not suc cessful in adapting them for use in large guns. But about 1885, M. Vieille. a French ordnance engineer, produced a satisfactory powder from coTloided gun-cotton which the French adopted wrapped are unquestionably stronger in a cir cumferential direction than those built up with steel hoops, but the wire wrapping makes it' difficult to secure adequate longitudinal rigidity in pieces of 35 calibres or more. As guns built up without wire wrapping are able to with stand initial pressures of 20 tons per square inch with a good margin of safety, as pressures of more than 17 tons caused too much erosion, and as wire-wound guns lacked rigidity (and therefore accuracy) unless very heavy, wire winding has not come into general favor, hav ing been adopted only by Great Britain. Since 1900 the improvements in gunnery methods, range-finding, the °spotting of hits," etc., have greatly extended the effective battle range. This in turn has had a marked effect on the maximum calibre of a ship's guns. Since the accuracy, range and destructive power of guns increase with the calibre, it is manifest that as. soon as range-finding and spotting are able to determine the fall of shot beyond the effective range of existing guns, a larger calibre is de manded and larger ships must be built, if neces sary, to carry the new weapons. We have now reached 16-inch (possibly 18-inch) guns and 42,000-ton battleships and there is no con vincing reason to believe that these are ulti mate limits.