Popular Science Monthly/Volume 58/March 1901/Throwing a High Explosive from Powder Guns
|THROWING A HIGH EXPLOSIVE FROM POWDER GUNS.|
THERE is now at Sandy Hook a battery of pneumatic torpedo guns, and another at the port of San Francisco, the largest of which have a caliber of fifteen inches and are capable of throwing a maximum charge of 500 pounds of nitro-gelatin about a mile. Even to attain this range, it is necessary to fire at a very high angle. The projectile has no power whatever of penetration, being only a thin casing, about an eighth of an inch thick.
The purpose of these guns was to drop dynamite upon the deck of war vessels, or into the water to explode near them. These batteries are necessarily provided with a large plant of engines, boilers and air compressors, which, together with the long and cumbersome pneumatic guns and mountings, present unusual difficulties in their protection from the fire of an enemy, while the range is so short that a modern battleship could approach within what, for it, would be a comparatively short range, and destroy the entire outfit, without in turn being in the least exposed to the fire of the pneumatic tubes. Even should a battleship, in order to enter the Channel, be obliged to pass within range of the pneumatic guns, it would be by mere chance that one of the torpedo bombs could be dropped anywhere near it.
We will grant, however, that should these guns score a hit, with 500 pounds of nitro-gelatin, thebattleship would have cause to tremble, especially should the bomb drop into the water and explode near the unprotected hull.
The pneumatic gun owes its existence to a misconception of the nature and possibilities of high explosives and of the requirements of a system for their successful projection from ordnance. Congress appropriated the money for the construction of the pneumatic batteries now in service from the same misapprehension of their utility. The 'Vesuvius,' with its pneumatic guns, was also the child of error. The shots fired by her at the fortifications of Santiago resulted in nothing more serious than the production of loud reports, which possibly frightened the enemy. Her projectiles had no power of penetration, and, therefore, were useless against fortifications.
It must be borne in mind, however, that the modern powder gun, with its small caliber and ponderous weight, throwing a heavy steel projectile, with but a small bursting charge of black powder, or with none at all, and the unwieldy armor-clad battleship are also only the children of experiment and have not yet passed the experimental stage. These constitute one extreme of the problem, while the pneumatic torpedo gun is the other. In the belief of the writer, the large-bored cannon for throwing high explosives at high velocity, propelled by smokeless gunpowder, instead of by compressed air, is a mean between the extremes, which is destined to solve the problem; while the present form of cannon and the armor-clad warship, on the one hand, will be relegated to the rear, and the pneumatic gun, on the other hand, will fall into oblivion.
It was with a view to the solution of the problem of successfully throwing high explosives from powder guns that the writer developed the progressive smokeless powder, which has been adopted by the United States Government, and by the use of which higher velocities with lower pressures are secured than would be possible by any other means. A special form of multi-perforated powder grains, invented by the writer, for throwing aerial torpedoes from guns, makes it possible to so control the pressures, even when full charges are employed, as to warrant the use of guns having a very large caliber and comparatively thin walls. I found that several high explosives could be made sufficiently insensitive to withstand the shock of acceleration in powder guns necessary to any desired velocity.
There was, however, at that time, no means known for making a fuse which should carry a sufficient quantity of detonative material, such as fulminate of mercury or a similar compound, in order to detonate effectually the insensitive high explosive charge on reaching the target. When such a quantity of fulminate was employed, there was danger of its being exploded by the shock of the propelling charge of gunpowder, and in turn setting off the high explosive charge of the shell and bursting the gun.
I designed and patented a fuse in 1895, in which the detonator was positioned at the rear of the shell, and completely outside of the high explosive charge, with the whole strong wall of the shell base between it and the high explosive, in which position, should the fuse go off prematurely from shock in the gun, the detonator would blow out at the rear and no damage would be done, as the high explosive would be beyond its reach. When, however, the projectile with its fuse struck the target, the body of detonative compound was thrown violently forward in a guide tube and into the high explosive bursting charge, due to the retardation of the projectile.
To carry out the foregoing experiments, I built two powder mills at Maxim, near Lakewood, N. J. It was there that the Maxim-Schüpphaus smokeless powder was produced, and there I conducted a large number of experiments with a long four-inch gun, having pressure gauges at different points along the whole length of the barrel, by which it was possible to ascertain not only how much pressure was exerted behind a projectile at the instant of firing, but how well the pressure was maintained behind it all along the bore. From this gun a torpedo shell, made thin and filled with Maximite and having a very heavy base portion filled with lead to act as tamping, was fired against an armor plate three and one-half inches thick and four feet square, demolishing it completely. The quantity of high explosive carried was only two pounds.
After the completion of the experiments at Maxim, N. J., and the successful testing of the Maxim-Schüpphaus powder by the United States Government, followed by its adoption, I went to England, with a view to the disposition of the foreign patent rights. On the 24th of June, 1897, I delivered a lecture before the Eoyal United Service Institution of Great Britain, on 'A New System of Throwing High Explosives from Ordnance.'
I explained and illustrated how a torpedo gun could be constructed which would weigh no more and cost no more than the ordinary twelve-inch seacoast rifle, but which should have a caliber twice as great, and which would stand a chamber pressure sufficiently high to throw a projectile carrying half a ton of high explosive at as great a velocity as that imparted to the usual 1,000-pound shell thrown from the 12-inch gun, and which carries only 37 pounds of black rifle powder.
I showed diagrams giving the range of destructiveness of such aerial torpedoes when striking in the water adjacent to a battleship, and claimed that such a quantity striking on board or against the armored side, under high velocity, would, without question, throw the vessel out of action.
This lecture was very widely commented upon in both the general and the scientific press, and it was stated in the House of Parliament, by one of the members who was opposing the appropriations for so many large battleships, that it would be necessary, in the event of war, and after the aerial torpedo was introduced, to keep battleships snugly in harbor and roof the harbors over to protect them.
The Gathmann Gun Company, last year, secured an appropriation from Congress for a large torpedo gun, which was constructed by the Bethlehem Ironworks, and now lies at the Sandy Hook Proving Grounds, awaiting tests.
This gun is very like that proposed by me in the above-mentioned lecture, excepting that the caliber is not quite so large for the weight, although the caliber, which is eighteen inches, will doubtless prove sufficient to enable the gun to give a good account of itself.
In the trials of this gun, made by the builders with a charge of Maxim-Schüpphaus smokeless powder, a projectile weighing a ton was hurled at a velocity of 1,900 feet per second with a pressure of only 19,000 pounds to the square inch. As the gun will safely stand a pressure of 25,000 pounds-to the square inch, a velocity of more than 2,000 feet per second can obviously be readily obtained, as against the velocity of from 2,000 to 2,250 feet per second for the 1,000 pound shell from the 12-inch gun, with a pressure of 35,000 pounds to the square inch. We must note here that the weight of the Gathmann gun is only 59 tons, against 52 tons for the 12-inch seacoast rifle.
A bill now before Congress calls for an appropriation for the efficient testing of this weapon. The service projectile, which will be thrown from this gun in the coming test, will carry about 475 pounds of wet, compressed guncotton, or 700 pounds of Maximite. Maximite being 50 per cent, heavier than guncotton, the shell will hold 225 pounds more of that material. There are to be 24 shots at full velocity, some for range and accuracy, and others to show the effect on powerful structures erected on the land. The last and final test will be against a steel barge anchored off shore, presenting a side fully armored and supported, so as to offer even greater resistance than would be afforded by the side of the strongest battleship now afloat.
Although Mr. Gathmann is my competitor, I feel much gratified at his success in procuring from the Government the necessary appropriations for building and testing this gun, and I am of the opinion that the results of these tests will prove a source of gratification to all the taxpayers of the country, who, unless the gun proves successful, will be called upon to contribute hundreds of millions of dollars for building and arming a fleet of monster battleships, which will not be required after one shot has been fired against the steel barge which will be provided for the purpose.
The war vessel that must follow as a natural result of the success of the aerial torpedo will be an unarmored, or only partially armored, gunboat or cruiser of small dimensions, capable of traveling at very high speed. It will be a sort of floating gun-platform, and will cost only a fraction of what the battleship costs, while a single one of these gunboats will afford far more protection than the most powerful battleship.
The United States Government has, during the last two years, been putting forth especial efforts to thoroughly investigate the qualities and merits of high explosives, with a view to finding the best bursting charge for shells. A large number of explosive compounds have been submitted by various inventors and tested by the Ordnance Department of the United States Army at the Sandy Hook Proving Grounds.
Some of the explosive compounds submitted have given very satisfactory results. Perhaps half a dozen of them would serve fairly well, if nothing better could be found. The Government, however, has placed its standard of excellence very high, with the hope of finding, if possible, something better than is possessed by other countries.
The United States Government was one of the last to adopt a smokeless powder, notwithstanding the fact that it was one of the first to experiment with these new explosives. But the Departments then having the matter in charge were very conservative, taking nothing for granted, were uninfluenced by the example of other countries and were determined that nothing but the best would be good enough for Uncle Sam. The result is that this Government to-day possesses a smokeless powder superior to that adopted by any other country. The same policy has been manifested in the search for a high explosive suitable as a bursting charge for shells.
The tests through which a high explosive must pass before there is the least hope of its meeting the requirements of the Government are very severe. The inventive Yankee, having an ambition to serve the Government by producing for its use a satisfactory high explosive, has u difficult task before him. In the first place, the compound must be perfectly stable, and to determine this it is submitted to a severe heat test for a period of fifteen minutes. If it fails to stand this test it is condemned at once, and goes no further. If it passes the heat test satisfactorily, a quantity is then placed under a falling weight or hammer to test its sensitiveness or its ability to resist shock. This is determined by the height from which it is necessary for the hammer to fall in order to explode the material. If the explosive proves sufficiently insensitive to indicate that it will stand the impact or shock of penetrating armor plate, it is then tested to determine its explosive power. A forged steel armor-piercing shell is filled with the material and armed with a very powerful exploder, which is set off by electricity. The force of the explosive is shown by the number and character of the fragments. Small shells are burst for fragmentation in a steel-walled chamber; larger shells are buried in the sand and exploded, the fragments being recovered by sifting the sand.
If the number of fragments indicates a sufficiently high explosive power, an armor-piercing shell is filled with the compound and fired through a nickel steel plate, so thick as to almost stop the shell in passing through, leaving just velocity enough to carry it a few feet into a sand butt back of the plate, where it may be dug out and recovered, provided the explosive proves to be sufficiently insensitive to stand the shock of impact, and does not explode on the instant of striking the plate. This is a very severe test—the severest of all. An explosive which will stand this impact on the plate, where the entire velocity of the projectile is overcome, while moving its length through the plate, is proved to be so insensitive that there can be no danger in its projection from ordnance at any desired velocity. That is to say. there will be no danger of the explosive going oil' in the gun, because the shock of acceleration in the gun is necessarily very much less than the shock of retardation when the projectile strikes the armor-plate.
Maximite has passed all of the above tests satisfactorily. When it was subjected to the heat test and no change was manifested at the
Twelve-inch forged steel armor-piercing shell, weighing 1,000 lbs., before and after exploding the Maximite. There are about 7.000 fragments shown in the photograph from which this illustration was made.
end of fifteen minutes—the required time—the material was allowed, at my request, to remain under the lest for a period of two hours, and there were no signs of decomposition even then.
A 12-inch forged steel armor-piercing shell, weighing 1,000 pounds, and provided with a detonating fuse, Inning electrical connections for tiring, was filled with Maximite. The shell was buried in the sand and exploded. So terrific was the detonation that 7,000 fragments were actually recovered and photographed.
The accompanying illustration. Fig. 1, shows the shell before exploding. On the right of the shell are 7,000 fragments which were recovered. It will he observed that the fragments do not have the usual broken appearance, but arc much distorted by the violence of the explosion.
A live-inch armor-piercing projectile was next filled with Maximite and fired through an armor plate, as above described, the projectile being afterwards recovered intact. It was found that the shock had in no way affected the explosive. The shell was then armed with a fuse and fired by electricity. The number and character of the fragments showed that the same force was developed in proportion to the weight of the shell, as in the case of the large 12-inch shell above mentioned, which was exploded in the sand. The five-inch shell is shown in Fig. 2. The fragments recovered after the explosion are shown on the right of the shell.
The next test was with projectiles filled with Maximite fired against
Five-inch forged steel armor-piercing projectile, weight 45 lbs., before and after exploding the Maximite. This shell, after filling with the explosive, was first fired through a four-inch nickel steel plate into a sand butt, where it was recovered intact. It was then exploded for fragmentation. There are a little over 800 pieces of the shell shown in the photograph, the average weight of the pieces being, therefore, about one ounce.
a concrete wall, with results which demonstrate that the power of the explosion was superior to that of any other high explosive ever thrown from a gun.
Projectiles loaded with. Maximite were then fired through a wooden screen, after passing which they exploded, and the fragments went into the sea. The fragmentation was such that the appearance of the water was similar to that which would be produced by the simultaneous fire of a regiment of musketry. On this occasion, a result was produced hitherto unknown, and which, perhaps, illustrated the violence of the explosive better than anything else. The projectiles, at the instant of explosion, were probably going at a velocity of about 2,000 feet per second. Pieces of the base plug of one of the projectiles were thrown back with such violence as to not only overcome the forward movement, but to throw them backward with a velocity estimated to be at least 1,000 feet per second.
This shows that a projectile filled with Maximite and exploded in a state of rest would have its fragments hurled at a velocity of about 3,000 feet per second, a much higher speed than that of a rifle ball, and that the forward-moving fragments, when a projectile is exploded in flight, will be hurled at a velocity something like 5,000 feet per second, or more than twice the speed of a rifle ball.
For the same reason that a large number of small bullets thrown at a high velocity are more effective and deadly than the large, heavy, slow-moving bullets formerly employed, a shell filled with such an
|Fig. 3.||Fig. 4.||Fig. 5.|
The fragments, natural size, of the point of a forged steel armor piercing shell, exploded with Maximite, showing the ragged and shredded state of the metal produced by the explosive, with the hardened tip of the projectile broken off by the impact.
Side view of a fragment from the body of a 12-inch armor-piercing forged steel shell, exploded with Maximite. On the left of the fragment, which was the inner surface of the shell, is seen the flattening and stretching effect of the blow which it received from the explosion, as though it had been heated and then struck with a sledge-hammer, the force of the blow being so sudden and severe that the whole outer surface of the shell, except a small piece seen hanging to the fragment on the right was knocked off by the force of the impact.
View of opposite side of fragment seen in Fig. 4, showing where this piece was jammed upon a neighboring fragment with such force that its surface «:i-made In flow like wax.
explosive as Maximite has an enormous advantage over explosives heretofore in use.
Maximite cannot be exploded by ignition. If a store-house filled •with this material were set on fire, there would he no danger of explosion. Melted cast iron may be poured upon a mass of Maximite without the least danger of exploding it. When heated, it melts, and if the heating be continued, it will evaporate like water, without producing an explosion. Lyddite, the high explosive adopted by the British Government, is said to be simply picric acid. This substance is melted for filling the shells, which are preliminarily heated to about the fusion point of the material to prevent too rapid setting. The melting point of picric acid is 122° C. The melting point of pure Maximite is exactly one-half of that of picric acid. That is to say, it is 01° C. The low melting point of Maximite enables it to be fused over the ordinary water bath, but owing to the impossibility of exploding it by heat, the water bath is not used, for it may be melted over an open fire in the same manner that asphalt is melted in the street cauldrons, and with equal safety. It is not necessary to heat the shells beforehand when filling them with Maximite.
On the other hand, great care has to be taken in the fusion of picric acid, because, if it becomes ignited in quantity before fusion, while in granular form, it will detonate, and also if it be heated very much above the fusion point, it will detonate.
The high fusion point of picric acid renders it necessary to employ a special lining material for protecting the shells against the erosive effect of the acid, while Maximite has very much less erosive action upon metals, and owing to its low fusion point an ordinary coating of shellac or similar substance is all that is necessary to protect the shells.
It has been found from the experiments made by the Government that, although a high explosive may be so sensitive as to safely with 1 stand the shock of acceleration in the gun. it may still be dangerous to fire, owing to the rapid rotation given to the projectile by the rifling of the gun, which is a rate of about 7,000 turns a minute. As a result, the projectile revolves upon the explosive before the latter has time fully to participate in its rotation. The great heat generated by this friction is apt to set fire to the explosive, causing a detonation.
Maximite requires so little heating for fusion that there is but slight contraction of the molten substance in reaching the point of solidification or freezing point. Maximite, furthermore, possesses the peculiar quality of expanding on solidifying, in the same way that Mater does on freezing. This causes it to set very firmly upon, and to adhere tightly to, the walls of the shell, so that it is quite impossible for the charge to shift in the shell. In the event, however, of the shell rotating upon the Maximite charge, the surface of the substance exposed would simply melt, producing a fluid and perfectly frictionless bearing. In the Transvaal War many Lyddite shells exploded prematurely, either from shock in the gun or from the rotation of the shell upon the charge. Such prematures would be impossible with Maximite.
Three 3-inch shells, which were filled with Maximite and primed with 50 grains of fulminate of mercury. The points of the shells were blown off with the fuse without exploding the Maximite. The confinement and the force of the exploder wore not sufficient to detonate the Maximite. This is a good illustration of the extreme insensitiveness of this material. (See small piles of unexploded Maximite below the fragments of the shells.)
When wet compressed guncotton is used as a shell charge, there is always some danger of a premature from the rotation of the shell upon the charge, especially when the percentage of water is not great.
Maximite is the first high explosive, satisfactory in other respects, which could be tired through armor plate of such thickness as to lender it available for armor-piercing shells.
In a recent test it the Sandy Hook Proving Grounds, a 12-inch armor-piercing forged steel shell, carrying a bursting charge of 70 pounds of Maximite. was fired through a 7-inch Harveyized nickel steel plate. This is the maximum thickness of such a plate for which this shell is adapted; hence Maximite has shown itself capable of withstanding the shock of penetration of armor plate as thick as the armor-piercing shell itself will stand, and furthermore, in the maximum quantity which the largest shells are capable of carrying.
In the 12-inch shell for piercing still thicker armor, the charge space is considerably smaller and the length of column of explosive very much shorter, so that, although the shock upon the projectile would be greater, still the shock upon the explosive would not be any more severe than that exerted upon the Maximite in the above test.
The writer has developed a fuse which will carry 100 grains, or even more, of a fulminate of mercury compound, together with more than 2,000 grains of a picrate, through the thickest armor plate, without going off prematurely, and which will act promptly to explode the bursting charge of Maximite immediately it gets through the plate.
A section of the common 12 inch seacoast rifle, and a section of torpedo gun proposed by the writer in a lecture before the Royal United Service Institution of Great Britain, June, 1897.
The problem of successfully throwing high explosives from powder guns may be said to be already solved. Not only this, but the far more difficult problem has been solved, of successfully firing high explosives through armor plate to explode inside of a war vessel.
An equally important feature of the problem has also been met, and that is the safety in storage of high explosives in quantity, especially in the magazines of a battleship. The refractory character of Maximite is such that it is rendered absolutely safe under such circumstances. Furthermore, it is so insensitive that projectiles filled with it could not be exploded by other projectiles striking them and exploding among them.
In a recent test by the Government, three 3-inch shells were filled with Maximite and armed with a point fuse filled with fifty grains of fulminate of mercury, and the fuses fired by electricity. As a result, the forward ends only of the shells were blown off by the fuse, leaving the whole rear portions of the shells unbroken, and filled with unexploded Maximite. The fragments of the forward ends, which were recovered, had the Maximite adhering to them like mortar to a brick. Another 3-inch shell was filled with picric acid, fused and fired in exactly the same manner as were the Maximite shells. The picric acid detonated with great violence, breaking the shell into small fragments. This test determined the superior insensitiveness of Maximite, and its absolute safety against even very severe shocks.
In order to effectually detonate Maximite, it must he confined in a very strong steel shell, and set off with net less than 100 grains of fulminate of mercury, reinforced with not less than 1,000 grains of some form of picrate, dry guncotton or similar substance.
In the recent tests made by the British government upon the old battleship, the "Belleisle," great havoc was found to have been wrought by the Lyddite shells whenever they penetrate through the ship's side at unprotected points, but all such shells which struck upon the armor plate exploded on impact, and did no damage. Had Maximite shells been used in this test, they would have passed through the armor plate and exploded inside the vessel.
Maximite is an entirely new chemical compound. Nothing like it, to my knowledge, has ever before been produced. Its production is based upon an entirely novel theory of detonation, which, together with the formula for the material itself, is kept a Government secret.