In commencing my paper this evening I desire to call your attention to
the fact that I am dealing with a subject which, though not
theoretical, is still hardly practical, for as a matter of fact high
explosives cannot be said to have yet been regularly used in warfare,
and I hope you will pardon me if in consequence my statements appear
in some respects unsatisfactory and my theories unsound. My subject,
however, is no more obscure than future naval warfare generally. All
civilized nations are spending millions of money for fighting purposes
directly in opposition to the higher feelings of the better class of
their inhabitants. The political atmosphere of Europe is the cause of
this, but its consequence is the development of theoretical plans of
ships which are no sooner commenced than the rapid march of
mechanical, chemical, and electrical science shows them to be faulty
in some particular feature, and others are laid down only to be
superseded in their turn.
None of these crafts are obsolete (to use the popular expression of
the day). All are theoretically better than any which have stood the
test of battle; but each excels its predecessor in some particular
feature. The use of high explosives is the direct cause of the very
latest transformations in marine architecture, and is destined to work
still greater changes; but it will require a war between the most
civilized nations of the world, and a long war, to either confirm or
condemn the many theoretical machines and methods of destruction that
modern science has produced. I say a war between the most civilized
nations, since it is only they that can supply the educated intellect
that is necessary to both attack and defense. Under other
circumstances false conclusions as to weapons and results are certain
to be drawn.
At the bombardment of Alexandria, the English armorclads, with their
rifled guns, were not nearly as efficient against the feeble chalk
fortifications as our wooden ships would have been with smooth bore
guns. On the other hand I saw on shore after the bombardment hundreds
of torpedoes and miles of cable that the Egyptians did not understand
how to use. The French war with China was equally unsatisfactory from
a military point of view. The Chinese at Foochow were annihilated
because the French opened fire first, and the only shell that
penetrated a French ironclad was filled with lamp black instead of
powder. The national riots that we are accustomed to hear of in South
America are likewise of little instructive value; they buy their
weapons of more civilized people, but there is always something
fatally defective about the tactics pursued in using them. It may be
said in general terms that in these days of extreme power in fighting
machines, the greater the efficiency the less the simplicity and the
more knowledge required in the care of the weapons. When powder was
merely powder the advice of the old adage to "trust in God and keep
your powder dry" was ample to maintain the efficiency of the powder
for all purposes; but nowadays if you keep your powder dry you will
burst your gun, and if you keep your gun-cotton dry you are liable to
blow up your ship.
It is rather difficult to-day to define what high explosives are, in
contradistinction to gunpowder. Thirty years ago we could say that
powder was a mechanical mixture and the others were chemical
compounds; but of late years this difference has disappeared.
The dynamical difference, however, still remains. Gunpowder in its
most efficient form is a slow-burning composition, which exerts a
relatively low pressure and continues it for a long time and to a
great distance. High explosives, on the contrary, in their most
efficient form, are extremely quick-burning substances, which exert an
enormous pressure within a limited radius. Ordinary black gunpowder
consists of a mechanical mixture of seventy-five per cent. of
saltpeter, fifteen per cent of charcoal, and ten per cent. of sulphur.
The most important of the high explosives are formed by the action of
nitric acid upon organic substances or other hydrocarbons, the
compound radical NO2 being substituted for a portion of the
hydrogen in the substance. The bodies thus formed are in a condition
of unstable equilibrium; but if well made from good material, they
become stable in their instability, very much like Prince Rupert's
drops, those little glass pellets which endure almost any amount of
rough usage; but once cracked, fly into infinitesimal fragments.
The power exerted by these nitro-substitution products is due to the
fact that they detonate, i.e., they are instantaneously converted into
colorless gas at a very high temperature, and in addition they have
almost no solid residue. Nitro-glycerine actually leaves none at all,
while gunpowder leaves sixty-eight per cent. The first departure in
gunpowder from the old-time constituents of black powder just
mentioned was for the purpose of obtaining less pressure and slower
combustion than could be produced by mere granulating or caking. This
was accomplished by using underburned charcoal, together with sugar
and about one and one-half per cent. of water. This is the brown
powder most generally used at present and with satisfactory results;
but the abstraction of its moisture increases its rapidity of
combustion to a dangerous degree, besides which the underburned
charcoal is itself unstable.
The next change demanded is smokelessness, and to accomplish it
recourse is had to the high explosive field, mechanically mixing
various substances with them to reduce and regulate their rapidity of
action. Just now some form of gun-cotton is most in use mixed with
nitrate of ammonia, camphor and other articles. The tendency of these
mixtures is to absorb moisture, and the gun-cotton in them to
decompose, and there is no smokeless powder which can to-day be
considered successful. Such a powder, however, will undoubtedly be an
accomplished fact in the near future. Military men seem to be a great
deal at variance as to its value in the field, but there can be no
doubt of its value for naval purposes; it is a necessity forced upon
us by the development of torpedo warfare.
First came the simple torpedo, at the end of an ordinary boat's spar.
Then came the special torpedo boat with its great speed, then the
revolving cannon and rapid-fire gun to meet the torpedo boat. At
present the possible rapidity of fire is much greater than can be
utilized, on account of the smoke; hence the necessity of smokeless
powder. Smokelessness is, however, principally a martial demand that
has been made upon the science of explosives and has attracted public
attention on that account. The commercial demands for various other
properties have been much greater than the military, and between
gunpowder near one end of the line in point of power and
nitro-glycerine near the other, there are now over 350 different
explosives manufactured, and most of these have been invented within
the last twenty years.
The simplest application of high explosives in warfare is in
connection with torpedoes, since within the same bulk a much more
efficient substance can be obtained than gunpowder, and with
reasonable care there is very little danger of premature explosions by
reason of accidental shocks.
Torpedoes were made by the Chinese many years ago, they were tried in
our war of independence, and also by the Russians during the Crimean
war; but the first practical and successful use of them as a
recognized weapon was during our war of secession, when thirty-seven
vessels were either sunk or seriously injured by them. Gunpowder was
used in these torpedoes, though it is stated that attempts were made
to use other substances without success. Since that time all maritime
nations have made a close study of the subject and have adopted
various high explosives, according to the results of their
experiments. In general terms it may be stated that explosive chemical
compounds have been found more suitable than explosive mixtures,
because of the uniformity of direction in which they exert their
pressure, and from the fact that water does not injure them. Mixtures
may be very powerful, but they are erratic and require tight cases. In
the United States we use dynamite for harbor mines. It is composed of
seventy-five per cent. nitro-glycerine and twenty-five per cent.
silica; but blasting gelatine and forcite gelatine will probably be
adopted, when they can be satisfactorily manufactured here, as they
are more powerful. The former is composed of ninety-two per cent. of
nitro-glycerine and eight per cent. of gun-cotton, and the latter of
ninety-five per cent. of nitro-gelatine and five per cent. unnitrated
cellulose.
For naval use we have adopted gun-cotton as being the most convenient.
In Europe gun-cotton is generally used for both fixed mines and
movable torpedoes; Russia, Austria, and Italy use blasting gelatine
also.
In actual warfare but little experience has been had. Two Peruvian
vessels were sunk by dynamite in the Chili-Peruvian war, one Turk by
means of gun-cotton during the Turco-Russian war of 1877, and two
Chinese by gun-cotton in the Franco-Chinese war of 1884.
In making experiments to determine the relative strength of the
different explosives under water, very curious and puzzling results
have been obtained. Nitro-glycerine being the simplest and most
complete in its chemical decomposition, and apparently the most
powerful in air, it was natural to suppose that it would be the same
in submarine work, but it was found by Gen. Abbot, at Willets Point,
after repeated experiments, as shown in his report of 1881, that it
was not so powerful in its effect by twenty per cent. as dynamite No.
1, although the dynamite contained twenty-five per cent. of an
absolutely inert substance. His idea was that it was too quick in its
action, and, since water is slightly compressible, a minute fraction
of time is required in the development of the full force of the
explosive. Gen. Abbot's results for intensity of action per unit of
weight of the most important substances is as follows:
Blasting gelatine........................... 142
Forcite " ........................... 133
Dynamite No. 1.............................. 100
Gun-cotton, wet............................. 87
Nitro-glycerine............................. 81
Gunpowder.............................. 20 to 50
Col. Bucknill, of the Royal Engineers, in his publication of 1888,
gives the following:
Blasting gelatine........................... 142
Forcite " ........................... 133
Dynamite No. 1.............................. 100
Gun-cotton, dry............................. 100
" " ............................. 80
Gunpowder................................... 25
In both tables dynamite No. 1 is assumed as the standard of
comparison. Col. Bucknill states that his gun-cotton results differ
from Gen. Abbot's, because he experimented with much larger
quantities, viz., 500-pound charges. Gen. Abbot's experiments led him
to believe that an instantaneous mean pressure of 6,500 pounds per
square inch would give a fatal blow to the double bottom of a modern
armorclad, and he developed a formula which gives this blow with
blasting gelatine at the following distances under water, viz.:
Pounds.
At 5 feet.................................. 4
" 10 " .................................. 17
" 20 " .................................. 67
" 30 " .................................. 160
" 40 " .................................. 311
Col. Bucknill's experiments caused him to believe that a pressure of
12,000 pounds per square inch is required, and his formula, which is
somewhat different from Abbot's, gives widely different results at
close quarters, but they approach each other as the distance
increases.
His results are as follows:
Pounds.
At 5 feet................................ 231/2
" 10 " ................................ 75
" 20 " ................................ 177
" 30 " ................................ 274
" 40 " ................................ 369
Regarding the comparative effects of gunpowder and the high
explosives, I think Gen. Abbot's estimate of a varying value for
powder is more admissible than the fixed value assigned by Col.
Bucknill. Gunpowder gives a push and detonating compounds a shock; as
the quantities increase, the push reaches farther than the shock.
According to Gen. Abbot, 100 pounds of dynamite No. 1 will have a
destructive horizontal range of 16.3 feet, while the same amount of
gunpowder will only have a range of 3.3 feet. Five hundred pounds of
dynamite, however, will have a horizontal range of 35 feet, and 500
pounds of gunpowder will have 19.5 feet; the ratio has diminished from
five to two. Whether 6,500 pounds or 12,000 pounds per square inch is
necessary to crush the bottom of an armorclad will depend largely upon
how far apart the frames of the ship are spaced and what other bracing
is supplied, as well as many local circumstances. It is difficult to
judge exactly of these matters. Some four years ago the Italian
government adopted treble bottoms for their heaviest ships as a result
of experiments with seventy-five pounds of gun-cotton (the charge of
an ordinary Whitehead locomotive torpedo) against a caisson which was
a _fac-simile_ of a portion of the proposed ships. Only two of the
bottoms were broken through, and when the space between the two inner
bottoms was filled with coal, only the outer bottom was broken.
According to the formulæ of either Abbot or Bucknill, there should
have been a local pressure of at least 300,000 pounds per square inch
on the outer skin, and yet judicious interior arrangements rendered it
harmless to the target. It would not, however, be safe to conclude
that the torpedo was thus vanquished; the immediate result was simply
to create a demand for larger locomotive torpedoes for local
application, and but little light was thrown upon the results which
might be anticipated from a large mine at a greater distance, whose
radius of explosive effect would embrace a larger portion of the ship,
and especially if the ship were nearly over the torpedo. The local
effect of a detonation is different from the transmitted shock.
Experiments in England have shown that 500 pounds of gun-cotton at
forty feet below any ship will sink her, and at a horizontal distance
of 100 feet, damage to the interior pipes and machinery is to be
expected.
The fact that the high explosives are so much heavier than gunpowder
has an important bearing on the size of the containing case. Their sp.
gr. is as follows:
Nitro-glycerine............................ 1.6
Blasting gelatine.......................... 1.45
Forcite " .......................... 1.51
Dynamite No. 1............................. 1.6
Wet gun-cotton............................. 1.32
Dry " ............................. 1.06
Gunpowder.................................. 0.9
Their relative efficiency under water per cubic foot, according to
Bucknill, is as follows:
Blasting gelatine.......................... 1.38
Forcite " .......................... 1.27
Dynamite No. 1............................. 1.00
Dry gun-cotton............................. 0.66
Wet " ............................. 0.66
Gunpowder.................................. 0.14
The wet gun-cotton has twenty-five per cent. of added water.
Mines for harbor defense are of two kinds--buoyant and ground. The
buoyant are usually spherical, and contain from 400 to 500 pounds of
explosive. They bring the charge near to the ship's bottom, but are
difficult to manage in a tideway, and can be easily found by dragging.
The ground mines can be made of any size and are not easily found by
dragging, but are of little value in very deep water. They are either
cylindrical or hemispherical in shape, and contain from 500 to 1,500
pounds of explosive in from thirty to eighty feet of water. Mines of
any kind are exceedingly difficult to render efficient when the water
is over 100 feet deep. On account of the tendency of all high
explosives to detonate by influence or sympathy, and the liability of
the cases to collapse by great exterior pressure, harbor mines are
separated a certain distance, according as they are buoyant or ground,
and according to the nature of the explosive.
Five hundred pounds buoyant gun-cotton mines require 320 feet spacing.
Five hundred pounds buoyant blasting gelatine mines require 450 feet
spacing.
Six hundred pounds ground gun-cotton mines require 180 feet spacing.
Six hundred pounds ground blasting gelatine mines require 230 feet
spacing.
Of torpedoes, other than those described, we have several modern
varieties; submarine projectiles, submarine rockets, automobile and
controllable locomotive torpedoes. The first two varieties, though
feasible, are not developed and have not yet advanced beyond the
experimental stage. Of the automobile, we have the Whitehead,
Swartzkopf and Howell. The first two are propelled by means of
compressed air and an engine; the last by the stored-up energy of a
heavy fly-wheel. Generally speaking, they are cigar-shaped crafts,
from 10 to 18 feet long and 15 to 17 inches in diameter, capable of
carrying from 75 to 250 pounds of explosive at a rate of 25 to 30
knots for 400 yards, at any depth at which they may be set. Of the
controllable locomotive torpedoes, the three representative types are
the Patrick, Sims and Brennan. They are in general terms cigar boats,
about 40 feet long and 2 feet in diameter, carrying charges of 400
pounds of explosive. The Patrick and Sims are maintained at a constant
depth under water by means of a float. The Brennan has diving rudders
like a Whitehead or a Howell. The Patrick is driven by means of
carbonic acid gas through an engine, and is controlled by an electric
wire from shore. The Sims is driven by electricity from a dynamo on
shore through a cable to an electric engine in the torpedo. The
Brennan is driven and controlled by means of two fine steel wires
wound on reels in the torpedo, the reels being geared to the propeller
shafts. The wires are led to corresponding reels on shore, and these
are rapidly revolved by means of an engine. A brake on each shore reel
controls the torpedo. The speed of all these torpedoes is about 19
knots, and their effective range one mile.
A Whitehead was successfully used in the Turco-Russian war of 1877.
The Turkish vessel previously mentioned was sunk by one.
Blasting gelatine, dynamite and gun-cotton are capable of many
applications to engineering purposes on shore in time of war, and in
most cases they are better than powder. They received the serious
attention of French engineers during the siege of Paris, and were
employed in the various sorties which were made from the city, in
throwing down walls, bursting guns, etc. An explosive for such
purposes, and indeed for most military uses, should satisfy the
following conditions:
(1) Very shattering in its effects.
(2) Insensible to shocks of projectiles.
(3) Plastic.
(4) Easy and safe to manipulate.
(5) Easy to insert a fuse.
(6) Great stability at all natural temperatures and when used
in wet localities.
Neither blasting gelatine, dynamite nor gun-cotton fulfills all these
conditions; but they satisfy many of them and are more powerful than
other substances. For the destruction of walls, trees, rails, bridges,
etc., it is simply necessary to attach to them small bags of
explosive, which are ignited by means of blasters' fuse and a cap of
fulminate of mercury, or by an electric fuse.
We now come to the application of high explosives to warfare in the
shape of bursting charges for shells. This is the latest phase of the
problem, and it is undoubtedly fraught with the most important
consequences to both attack and defense. Difficult as it has been to
obtain an exact estimate of the force of different explosives under
water, the problem is far greater out of the water and under the
ordinary conditions of shell fire; the principal obstacle being in the
fact that it is physically impossible to control the force of large
quantities in order to measure it, and small quantities give irregular
results. Theoretically, the matter has been accomplished by Berthelot,
the head of the French government "Commission of Explosives," by
calculating the volume of gas produced, heat developed, etc.; and this
method is excellent for obtaining a fair idea of the specific pressure
of any new explosive that may be brought forward, and determining
whether it is worth while to investigate it further; but the
explosives differ so much from each other in point of sensitiveness,
weight, physical condition, velocity of explosive wave, influence of
temperature and humidity, that we cannot determine from mere
theoretical considerations all that we would like to know. Various
methods of arriving at comparative values have been tried, but the
figures are very variable, as will be seen by the following tables.
Berthelot's commission, some ten years ago, exploded ten to thirty
grammes of each in 300 pound blocks of lead and measured the increased
size of the hole thus made. The relative result was:
No. 1 dynamite 1.0
Dry gun-cotton 1.17
Nitro-glycerine 1.20
Powder blew out and could not be measured.
Mr. R.C. Williams, at the Boston Institute of Technology, in the
winter of 1888 and 1889, tried the same method, but used six grammes
in forty-five pound blocks of lead. He obtained a relative result of--
No. 1 dynamite 1.0
Dry gun-cotton 1.37
Nitro-glycerine 2.51
Explosive gelatine 2.57
Forcite gelatine 2.7
Warm nitro-glycerine 2.7
Gunpowder 0.1
The powder gave great trouble in this case, also, by blowing out.
M. Chalon, a French engineer, obtained some years ago, with a small
mortar, firing a projectile of thirty kilos and using a charge of ten
grammes of each explosives, the following ranges:
Meters.
Blasting powder 2.6
No. 1 dynamite 31.4
Forcite of 75 per cent. N.G. 43.6
Blasting gelatine 45.0
Roux and Sarran obtained by experiments in bursting small bomb shells
the following comparative strengths of ranges:
Powder 1.0
Gun-cotton 6.5
Nitro-glycerine 10.0
In actual blasting work the results vary altogether with the nature of
the material encountered, and with the result that is desired to be
accomplished, viz., throwing out, shattering, or mere displacement.
Chalon gives for quarrying:
Powder 1
Dynamite No. 2, containing 50 per cent. nitro-glycerine 3
For open blasting:
Dynamite No. 3, containing 30 per cent. N.G. 1.0
Dynamite No. 1, containing 75 per cent. N.G. 2.5
Blasting gelatine 3.5
For tunneling:
Dynamite No. 3, containing 30 per cent. N.G. 1
Dynamite No. 1, containing 75 per cent. N.G. 3
Explosive gelatine 19
Finally Berthelot's theoretical calculations give a specific pressure
of--
Powder 1
Dynamite 13
Gun-cotton 14
Nitro-glycerine 16
Blasting gelatine 17
It will be observed that the practical results vary largely from the
theoretical values, but they seem to indicate that gun-cotton and No.
1 dynamite are very nearly equal to each other, and that in the
nitro-glycerine compounds, except where gun-cotton is added, the force
appears to be nearly in proportion to the nitro-glycerine contained.
From the foregoing it seems fair to estimate roughly the values of
bursting charges of shells as follows:
Powder 1
Gun-cotton and dynamite 6 to 10
Nitro-glycerine 13 to 15
Blasting gelatine 15 to 17
Attention has been turned in Europe for more than thirty years toward
firing high explosives in shells; but it is only within very late
years that results have been reached which are claimed as
satisfactory, and it is exceedingly difficult to obtain reliable
accounts even of these. Dynamite was fired in Sweden in 1867 in small
quantities, and a few years later it was fired in France. But two
difficulties soon presented themselves. If the quantity of
nitro-glycerine in dynamite was small, it could be fired in ordinary
shells, but the effect was no better than with gunpowder. If the
dynamite was stronger in nitro-glycerine, it took but a small quantity
to burst the gun.
As early as 1864, dry gun-cotton was safely fired in shells in small
quantities, but when a sufficient quantity to fill the shell cavity
was used, the gun burst. Some few years ago it was found that if the
gun-cotton was either wet or soaked in paraffin, it could be fired
with safety from powder guns in ordinary shells, provided the quantity
was small in proportion to the total weight of the shell--say five or
six per cent. But a new difficulty arises from the fact that it breaks
the shell up into very small pieces, and it is an unsettled question
among artillerists whether more damage is done to an enemy by breaking
a shell into comparatively large pieces and dispersing them a long
distance with a bursting charge of powder, which has a propulsive
force, or by breaking it with a detonating compound into fine pieces,
which are not driven nearly so far. When used against troops there is
also the objection to the high explosive shell that it makes scarcely
any smoke in bursting, and smoke at this point is useful to the
artillerist in rectifying his aim.
In the matter of shells for piercing armor, however, there are no two
opinions regarding the nature of the bursting charge. To pierce modern
armor at all a shell must be made of forged steel, so thick that the
capacity of the cavity for the bursting charge is reduced to
one-fourth or one-fifth of what it is in the common shell; the result
is that a charge of powder is frequently not powerful enough to burst
the shell at all; it simply blows the plug out of the filling hole in
the rear. In addition it is found that in passing through armor, the
heat generated is so great that the powder is prematurely ignited.
If then we can fill the small cavity in the shell with an explosive
which will not ignite prematurely, and yet will burst the shell
properly after it has passed through the armor, the problem will be
solved. Wet or paraffined gun-cotton can be made sluggish enough to
satisfy the first condition; but at present the difficulty is to make
it explode at all. The more sluggish the gun-cotton, the more powerful
must be the fuse exploders to detonate it, and such exploders are
themselves liable to premature ignition in passing through the armor.
The Italians and Germans claim to have accomplished the desired result
up to a thickness of five inches of armor; gun-cotton and fuse both
working well. But the English authorities say that no one has yet
accomplished it. The Austrians claim to have succeeded in this
direction within the last year with a new explosive called ecrastite
(supposed to be blasting gelatine combined with sulphate or
hydrochlorate of ammonia, and claimed to be one and one-half times as
powerful as dynamite).
With a gun of 8.24 inches caliber and an armor-piercing shell weighing
206.6 pounds, containing a bursting charge of 15.88 pounds of
ecrastite, they are said to have perforated two plates four inches
thick, and entered a third four-inch plate where the shell exploded.
There is a weak point in this account in the fact that the powder
capacity of the shell is said to be 4.4 pounds.
This amount is approximately correct, judging from our own eight-inch
armor-piercing shell, but if this is true, there could not have been
more than nine pounds of ecrastite in the shell instead of sixteen, or
else there is an exceedingly small proportion of blasting gelatine in
ecrastite, and if that is the case it is not one and one-half times as
powerful as dynamite. If it is weak stuff, it is probably insensitive,
and even if it were strong, one swallow does not make a summer. The
English fired quantities of blasting gelatine from a two-inch
Nordenfeldt gun in 1884, but when they tried it in a seven-inch gun,
in 1885, they burst the gun at once.
I have only analyzed this Austrian case, because the statement is
taken from this year's annual report of the Office of Naval
Intelligence, which is an excellent authority, and to illustrate the
fact that of the thousands of accounts, which we see in foreign and
domestic newspapers, concerning the successful use of high explosives
in shells, fully ninety per cent. are totally unreliable. In many
cases they are in the nature of a prospectus from the inventors of
explosives or methods of firing, who are aware of the fact that it is
almost impossible to dispute any statements that they may choose to
make regarding the power of their new compounds, and thinking, as most
of them do, that power alone is required.
Referring to the qualities that I have previously cited as being
required in a high explosive for military purposes, it is sooner or
later found that nearly all the novelties proposed lack some of the
essentials and soon disappear from the advertising world only to be
succeeded by others. The most common defect is lack of keeping
qualities. They will either absorb moisture or will evaporate; or
further chemical action will go on among the constituents, making them
dangerously sensitive or completely inert, or they will separate
mechanically according to their specific gravities.
For further clearness on the subject of the shell charges which have
so far been discussed, the following table is added of weight and
sizes of shells for United States naval guns, with their bursting
charges of powder:
6-inch com. cast steel shell 31/2 to 4 cal. long, wt. 100 lb., charge 6 lb.
8 " " " " " 250 " 141/2 lb.
10 " " " " " 500 " 27 "
12 " " " " " 850 " 45 "