Previous to 1872, most of the experimental ordnance work of the Navy was done at the Washington yard, and tests of powder were made there also, or at the powder yards, forts and arsenals.
In 1873, at the suggestion of Lieutenant-Commander Marvin, since deceased, the Government secured the lease for 99 years of a tract of land, comprising about 85 acres, on the Severn river, opposite Annapolis. The site was well adapted for the work on hand and in contemplation at that time, but, as will be seen, with the long range guns and the multifarious ordnance tests and experiments with high explosives which have attended the development of the new armament, the location of the Ground is in the highest degree unsuitable. Congress has appropriated $40,000 for the purchase of a new site, but the Bureau of Ordnance has not yet succeeded in finding a desirable place, although diligent search has been made.
The Ground is situated on a peninsula, the southern point of which is about woo yards from Greensbury Point lighthouse. The line of fire is directly down the bay, and it is impossible to exaggerate the disadvantages of the over-water range. In the winter months the range is obstructed by oyster boats, and the rest of the year by crabmen and pleasure parties from the neighboring summer resort at Bay Ridge. Unfortunately, the weather most favorable for firing down the bay is also that for these small craft, and the consequence is frequent long and tedious delays. It is obvious that ranging the new guns has been done under circumstances most trying to patience. It is only under exceptional circumstances that loaded shell can be fired over the range for testing fuzes; and the recovery of the shell for the purpose of examining the band or noting the action of the percussion fuzes is entirely precluded unless they are fired into the butt. The proximity of the lighthouse on Greensbury Point and the large hotel at Bay Ridge, and the danger to life and property from projectiles which occasionally escape from the butt, are further reasons why the present site of the Proving Ground should be changed.
The principal features of the station are the chronograph house, machine shops, Hotchkiss, velocity and range batteries, explosion chamber, small arm range, and the butt. A brief description of each will not be inappropriate.
The chronograph house contains three Boulenge instruments, and is at a sufficient distance from the batteries to protect the chronographs from the concussion of the heavy guns. The chronographs are mounted on heavy oak pedestals which rest on solid foundations of concrete and granite. The three instruments are used simultaneously when observing velocities from the heavy guns, but usually only one is placed in circuit with the Hotchkiss battery. It is the rule of the station to throw out a reading which differs as much as twelve feet from the mean of the other two.
The machine and carpenter shops, the forge, the engine and boiler rooms are under one roof. The machine shop contains three lathes, two planers, and the usual outfit of machinist's tools.
The Hotchkiss battery is located a few yards from the chronograph house, and is simply an uncovered heavy oak platform to which are bolted the mounts of the revolving and R. F. guns. In front of this battery are two small sand butts, one for catching the projectiles when firing for velocity, and the other when firing at plates.
The velocity battery is the main battery of the Proving Ground, and upon it the heavy guns are mounted for proof, testing powder, armor trials, and other work except ranging. The platform is made of heavy oak beams braced with horizontal diagonal wooden braces and strongly anchored to condemned guns and old armor plates. It is 28 feet above mean low water. The first gun, a 12-pounder howitzer, was fired from this battery on the i6th of April, 1873. In the following month the battery was completed and a 13-inch shot with a charge of 6o pounds was fired into the butt. The butt is thrown up 300 feet in front of the platform and runs parallel with it; it is 100 feet long, 40 feet high, and 69 feet thick; this thickness is sufficient to retain a 10-inch projectile fired with full service charge.
The range battery, erected on the site of Old Fort Lot, is near the water's edge on the bay front. It is used for ranging, principally, and has attached to it one set of velocity screens. It has an unobstructed line of fire down the bay. The explosion chamber is sunk in the side of the hill near the creek. Its walls, floor and roof are constructed of iron plates. A narrow tunnel leads to the entrance, which is a turret gun-port. Gas escapes are provided. The chamber is used for bursting loaded shell at rest when it is desired to observe the effects of bursting charges or the numbers and characters of the fragments of a particular kind of shell. The shell is suspended from an eye-bolt in the roof; fitted with an electric fuze and exploded by a Farmer's dynamo.
The magazine, which usually contains from 20,000 to 30,000 pounds of powder, is on the bank of the creek some distance in rear of the velocity battery. Near it is the filling house where the cartridges are made up.
In the "howitzer house," once the deck-house of the Saratoga, are stored the spare articles, and recently a flying shed, open to the southward, has been erected for sighting the guns, a work sometimes done at the station by mechanics from the Washington yard.
The dynamite house is a small brick building placed in a remote corner of the grounds. In it are kept dynamite, wet and dry gun cotton, and the fulminate of mercury igniters.
The small-arm range extends diagonally through the grounds and is 700 yards long. Concrete platforms are erected at intervals of 100 yards, and in testing small-arms for accuracy the gun is mounted in a rest placed on the platform. The target is to feet x 15 feet and is laid off in 6-inch squares, with several circles grooved in the center.
There is a Cobb dock on Little Carr Creek, and a channel has been buoyed for the entrance of scows and barges with heavy material.
There are no cranes, derricks, heavy transporting trucks or any of the facilities for handling and purchasing heavy weights; all such work is done with the meagre resources of the station, but under the intelligent and capable supervision of the gunners attached to the station, remarkable time has been made in transporting guns, etc., using manual labor assisted by such sailor-like devices as have been from time to time suggested by necessities constantly arising. With nothing but jacks, hawsers, and gun-wheels, two horses and the laborers—usually about 45—the 10-inch gun No. 1, weighing 55,000 pounds, was gotten out of the scow and parbuckled up the hill from the dock in about 24 working hours. This time was further improved when to-inch gun No. 2 was landed and hauled to position in 12 hours. A 6-inch gun weighing 11,000 pounds has been dismounted from its carriage and another mounted in a little more than one hour, using an improvised derrick. Heavy armor plates are handled in the same way, transported, lifted, and secured in place by means of jacks and tackles. In mounting 10-inch gun No. 1 on the turret carriage it was necessary to jack the gun up 13 ½ feet above the ground, roll it in position over the slide, and then lower it in place. As there is only a play of .02 inch between the straps on the gun and the lugs on the slide, the greatest care was necessary, and it was accomplished without accident, in two days.
The station was originally known as the Naval Experimental Battery, but the development of the new armament made the station something more than experimental, and in 1884 the name was officially changed to Proving Ground. The work of the station embraces the test and proof of service and other guns, ranging, test of carriages and mounts, projectiles and powder, trials of armor plates, ballistic tests of castings, experiments with high explosives as applied to powder guns, tests of primers, fuzes, ammunition returned from ships, etc.
PROOF OF GUNS.
Guns when finished at the Washington yard or at other foundries are sent to the station to be proved before issue to service. The 6-inch guns are sent by rail to Annapolis, hauled through the town, and taken across the river on a scow. The heavier guns are sent all the way by water. The Bureau requires four rounds to be fired with service charges and projectiles brought up to weight; the chamber pressure to be 15 tons per square inch, and the initial velocity of the projectile 2000 f. s. The gas-check disks and pads are fitted during proof. The gun is star-gauged before and after proof, and it may be interesting to note the fact that often after proof the chamber of the gun is smaller than before, sometimes by .001 in. or .002 in. This may be due either to the stretching of the tube longitudinally or to the closer grip which the jacket and A hoops are supposed to exert upon the tube when they recover from the transverse expansion caused by the pressure of gases in the chamber. The statutory test of ten rounds, fired as rapidly as possible, is applied to only one gun of each caliber. As yet none of the new guns have been tested to destruction.
Besides the proof of service guns, trials of special types which from time to time have been sent to the Proving Ground, have been conducted and the various systems submitted to exhaustive tests. Among these may be mentioned the Maxim machine-gun of .45 caliber, the Driggs-Schroeder 3-pounder and 6-pounder rapid-fire guns, and the cast-steel guns.
A good idea of the general arrangement and appearance of the Maxim gun is given by the photograph. The length of the gun over all is about 3i feet, and the height of the trunnions from the base of the reservoir is about 3 feet. It may be said to consist of three principal parts: the barrel, the box containing the loading and firing mechanism, and the reservoir. As is well known, the principle of the gun is the old one of utilizing the recoil for loading and firing; its action suggests perpetual motion. The barrel is enclosed in a waterjacket automatically fed from the reservoir by the firing of the gun. The reservoir holds sufficient water for eight minutes' steady firing, or 4800 rounds. The water is kept under a pressure of two atmospheres. The square box in rear contains the mechanism, which is very simple, but unnecessary to describe here. The gun is fed from a belt which holds the cartridges. To throw the gun in action it is only necessary to enter the belt and press the firing springs on the rear face of the box, and the firing will continue as long as the spring is kept pressed down. The entire action is automatic; the cartridges are taken from the belt, forced into the barrel, fired, withdrawn, and ejected by the recoil of the gun; by tailing on belts the gun will fire as long as desired. It will be observed that if there is a miss-fire the whole action ceases, obviating all danger of accident from "hangfires." During action the only motion visible is the in and out motion of the end of the barrel outside the water-jacket, the rapid forward and reversed motion of the bell-crank lever on the side of the box, and the steady advance of the belt across the reel. The gun is a marvel of simplicity and ingenuity and possesses many advantages. It has not yet been adopted by this government. It was tested at the Naval Ordnance Proving Ground last year. 3000 rounds were fired continuously, and the action noted for failures to fire, effect of heating, range, of rapidity of fire, velocity, accuracy as compared with the short Gatling, and its volley-power as compared with the same gun, and, finally, its endurance under the sand test. A new type of the Maxim rifle caliber gun has recently been tested at the Proving Ground, together with a 1-pounder R. F. gun. The new gun differs from the old principally in having a much larger cooling-chamber or water-jacket, which does away with the reservoir. This jacket holds about 2 ½ quarts of water, which is sufficient for the gun to discharge moo rounds in quick succession, but if fired in volleys the supply will suffice for z000 rounds. The Maxim .45 caliber fires 600 to 700 rounds per minute. At the N. O. P. G. last June the Maxim I-pounder discharged 100 rounds in 43.3 seconds.
The Driggs-Schroeder 3-pounder and 6-pounder R. F. guns have been tested at the P. G. with excellent results, and promise to become a formidable antagonist of the Hotchkiss guns which have for so long held the field undisturbed. The 3-pounder fired at the rate of 23 rounds per minute and the 6-pounder discharged 19 aimed shots per minute.
The Driggs Ordnance Co. have received a contract from the Bureau of Ordnance to apply this breech mechanism to the new 4-inch and 6-inch R. F. guns building at the Washington Navy Yard, and they have also received an order for a 6-pounder for the army.
RANGING.
Two range tables are computed for each caliber of the new guns, one for an initial velocity of 1700 f. s., the other , for 2000 1. s. The data for the computations is obtained by actual firing in the following manner :—The quadrant angle is calculated for ranges, say as in the case of ranging the 8-inch B. L. R., initial velocity 17oo f. s. for 3000, 4000, 5000, and 6000 yards. The gun is laid by gunner's quadrant, and about five shots are fired under service conditions at each of these elevations, the jump being observed, if possible, at each round. One observer with theodolite in rear of the gun observes the deflection of the splash from the line of fire, another notes the time of flight with a stop-watch, while three observers at stations on the shore line of the bay angle on the splash with plane tables. The "firing data" thus obtained is worked up into the range tables by Siacci's method. The table must contain the angle of elevation, height of sight-bar, time of flight, deflection, angle of fall, and remaining velocity for every 100 yards; the height of sight-bar for every ½ second of time of flight, and the range and height of sightbar in inches for every 30 feet of elevation.
TEST OF GUN CARRIAGES.
Gun carriages are tested for strength, rigidity and steadiness; the length, velocity and general character of the recoil and counter recoil, the amount and character of the strains on the deck circles, pivots, clips and rear trucks; the time required for loading, firing and training through various arcs; the behavior of the carriages when firing at extreme elevation and depression. To determine the velocity of recoil, a simple and ingenious instrument called a velocimeter has been designed by Ensign R. B. Dashiell, U. S. Navy. It consists of a frame supporting a heavy paper-covered cylinder 30 inches long and 12 inches in diameter, which revolves on its axis in accurate journals on the frame-work. Sliding on the frame and tracing an element of the cylinder when at rest, is a pencil which is connected with the gun by an iron rod in such a manner that any movement of the top carriage will give the same movement to the pencil point. The cylinder is revolved by a cord and falling weight, and its velocity of revolution is measured by noting with a stop-watch the time required for the weight to fall a fixed distance. At the lowest point of fall reached by the weight is a trigger by which the gun is fired and the acceleration is thus removed from the revolving cylinder simultaneously with the beginning of recoil, so that during the short interval of recoil the velocity of revolution may be considered constant. A curve is thus obtained from which the velocity of recoil can be measured at any point. In the diagram, a curve of recoil of a 6-inch gun is shown. The horizontal lines are distances travelled by the gun in the times indicated by the corresponding dotted lines. Several different types of gun-'carriages have been tested at the Proving Ground, the gravity return system giving the best results. The to-inch turret mount (hydraulic) is still under trial, and experimental firing has been done with the 8-inch B. L. R. on a pneumatic carriage.
POWDER.
Brown prismatic powder is used in all the heavy guns, black square grain powder in the rapid-fire guns, and fine grain black powder in the revolving cannon. These powders are manufactured by the Duponts at Wilmington, Del. At the Proving Ground all powder is submitted to two tests, one to ascertain its ballistic qualities and the other its physical properties. The specific gravity as a rule is determined at the powder yard, but it is occasionally verified at the Proving Ground. Mallet's densimeter is used for fine grain powder, and Dupont's densimeter for prismatic powder. The gravimetric density of fine grain powder only is taken. The amount of moisture it contains is determined by noting the decrease in weight of a certain amount which has been left in the drying stove until its weight is constant. Conversely its capacity for absorbing moisture is obtained by observing the increase in weight of a certain amount left in the water box until its weight is constant.
The ballistic qualities of a sample of powder are determined by the chronographs and pressure gauge. In the heavy guns three crusher gauges are screwed into the face of the mushroom, but in the rapid-fire guns one gauge is dropped loosely into the cartridge case. Sometimes—as in the 1-pounder, the case of which is too small to hold the charge and gauge—the gauge is screwed into the base of the projectile. When this is done, 50 per cent of the observed pressure must be added to give the chamber pressure. This method is, however, unreliable.
The specifications of all the new heavy guns and the 3-pounder rapid-fire gun require an initial velocity of 2000 f. s. with a chamber pressure of 15 tons per square inch. The specifications for the powder of other guns vary according to the type of gun, but 15 tons per square inch is the maximum pressure allowable in any gun.
In testing a sample of powder it is usual to begin by firing about half the service charge. The charges are made up by hand, and the operation is rather long, 15 minutes being required for a 6-inch charge and about 25 minutes for an 8-inch charge of 126 lbs. The pressure and velocity obtained from this round serve as a guide by which to work up to the required velocity and pressure.
The development of powder for the new guns has been carried on at the Proving Ground. In 1884 the Duponts succeeded in making the first satisfactory brown prismatic powder which gave as good if not better results than the German powder. The powders for the 5, 6 and 8-inch calibers have been determined, but that for the 10-inch is still in the experimental stage.
The record of official powder samples is kept by a system of letterings in such a way that if the letter of the powder is known, the gun for which it is intended is also known. The P. V. A., P. V. B., etc., are 5-inch powders, 0. P. A., 0. P. B., 0. P. C. are 6-inch, and R. G., R. G. A., R. G. B., 8-inch. These letters are not abbreviations and have no other significance than to designate the powder for a particular caliber.
The bursting of the gun on the Admiral Duperre has raised the question of the effect of continued high temperature on brown powder—the supposition being that when the moisture is dried out the powder becomes very much quicker. The subject will soon be investigated at the P. G. A box has been constructed, the temperature of which will be maintained at 140° F. The I. V. and the pressure of a sample of powder will be determined before it is stowed in the box, and again after it has been subjected to the high temperature for several months.
TEST OF PROJECTILES, ARMOR PLATES, PRIMERS, FUZES, ETC.
Projectiles are tested with reference to temper, toughness, action of band, shape of head for various work, character of flight, etc. Cast-iron, cast-steel and chrome-steel shell have been tested in the new guns. In January, 1889, an 8-inch tempered steel shell was fired against a 10-inch compound (Cammell) plate. The plate was 298 .feet from the muzzle of the gun, and the striking energy of the projectile was 6794 foot-tons. The projectile pierced the plate, but broke up, all the fragments remaining in the plate and backing. The head of the projectile was considerably upset. The hard face of the plate was broken off around the impact to a depth of one to two inches. Seven large cracks were opened. The appearance of the plate is shown in the photograph.
Plates and shields are tested for resistance when tempered by different methods. The ballistic test of armor plates of more than 6 inches is in general terms the following: The plate will be bolted to wooden backing of 36 inches. Near the middle of the plate will be laid off an equilateral triangle, the length of each side being 3 ½ calibers of the gun to be used in the test. The velocity of the projectile will be such as gives by calculation sufficient energy to pass through a wrought-iron plate and its wooden backing; the wrought-iron plate being supposed to be equal in thickness to the test plate. No projectile nor any fragment of the plate must get wholly through the plate and backing. The plate must not break up and pieces be displaced so as to expose the backing before the impact of the third shot; neither must very large cracks which expose the backing appear before the impact of the third shot.
The action of fuzes is observed with reference to their safety, liability to prematures in the bore, and for sensitiveness to explode on ricochet. Primers are tested for certainty of fire, leaks, and liability of fouling or spiking the vent.
EXPERIMENTS WITH HIGH EXPLOSIVES.
These have been of a tentative character, principally with the object in view of settling decisively the question of the safety of using wet and dry gun-cotton as a burster in shell fired from powder guns, and have included the experiments with the Torpedo Station mixture known as "Explosive A" and the Smolianinoff "inert" nitroglycerine. It is pretty certain that wet gun-cotton can be safely used as a bursting charge, but the question is still an open one.
"Explosive A" was a liquid which was poured into the shells. Eight rounds were fired successfully from the South Boston 6-inch steel gun; the ninth shell exploded in the gun, destroying the gun and wrecking the carriage.
The Smolianinoff experiments were discontinued after three rounds from the 8-inch M. L. R., as the last shell exploded unexpectedly on impact with the water.
PHOTOGRAPHY.
Photography forms an important part of the work at the Proving Ground, and is used almost daily to illustrate the official reports of the Inspector.
In 1884 an important modification was made in the English method of photographing the bore of a gun, by which pictures were obtained of desired points of normal size. This was accomplished by inserting the camera itself in the bore, whereas the foreign method was to photograph from the extremity of the gun, the camera being placed either at muzzle or breech, an arrangement which necessarily gave very small images on the ground glass. Experiments have been made to photograph a projectile at the instant of impact against a plate, but as yet have not been successful.