Introduction
IT IS generally conceded that the three outstanding military advances of the World War were the combat airplane, the military tank, and chemical warfare. Each of these new weapons was introduced at about the same time, each played an important role in modifying the characteristics of modern land combat, and each promises to command an even greater influence in future warfare.
The development of chemical warfare has been marked by two distinct stages: (1) There was the period of over 3 years of war when the basic foundations were laid in fundamental chemical research, large- scale production of gases, and the technique and tactics of offense and defense. (2) There followed the post-war period of continued research, development, and assimilation by the principal powers. As a result significant advances over the means and methods of the World War have been accomplished. In fact, it may be said that today chemical warfare is a firmly established arm of modern armies.
One is reminded at this point that chemical attack was not initiated by any of the navies in the World War. The principal reason for that situation appears to be that there are peculiar difficulties inherent in gas warfare as applied to sea forces; indeed certain tactical methods with gas are obviously impracticable. This uncertainty of effective attack at sea by a new and untried instrument was in all probability a dominant factor.
However, the success of chemical tactics on the Western Front, their subsequent progress, the ready availability of chemical intermediates for gas production and, above all, the tremendous development of military aircraft have led the principal navies of the world to recognize the imperative need for protective measures against gas. The purpose of this paper is to present certain aspects of the development of chemical warfare agents in relation to sea forces.
The Criteria for an Effective Chemical Warfare Agent
The term “gas”.—The chemical warfare agents may be in the physical state of true gases, solids, liquids, or smokes when released. Still the term “gas” has acquired a generic meaning in the military services embracing any chemical used for its physiological effect without regard to the form in which dispersed. Although inadequate in a technical sense, it is expressive and brief, and has a generally understood meaning by usage. Unless otherwise qualified the term is synonymous with any chemical warfare agent.
In the main these chemical agents are complex organic substances with lengthy chemical and short common names but are most concisely designated by the chemical warfare symbols adopted by the Chemical Warfare Service of the United States Army, such as PS for chlorpicrin or M-1 for Lewisite.
It should be remembered that the selection of a chemical which will meet the criteria necessary for effective use on the battlefield is extremely difficult. These requirements are so rigid that very few chemicals possess even the essential physical properties aside from the necessary physiological power.
If gaseous in the natural state, it is essential that it be capable of liquefication at moderate pressure and ordinary temperature, so that it can be loaded into munitions in adequate amount. Carbon monoxide, for instance, although a highly toxic gas cannot be readily liquefied and so is excluded as a war gas. Regardless of whether the chemical is in the form of a gas or a smoke, it must have a vapor density greater than that of air; otherwise on release it will immediately rise from the surface of the ground. Hydrocyanic acid gas is one of the most powerful lethal agents but is lighter than air. Its field use was attempted by the French on an extensive scale in the World War without success.
A high degree of toxicity or irritant effect is naturally required and, in general, the greater the number of physiological effects a gas produces, the more valuable it is in a tactical sense. For example, mustard gas has a triple effect, being a vesicant, lung irritant, and lachrymator. On the other hand, phosgene acts only as a lung irritant, although extremely lethal.
The chemical must be stable under all conditions of storage and must not corrode iron or steel containers. A highly effective tear gas known as brombenzylcyanide was utilized to a limited extent in the World War but has since been discarded for the reason that special linings of glass or porcelain are required in loading projectiles to avert corrosion. The compound should not break down readily on contact with moisture and it must resist within certain limits the high temperatures and pressures generated in dispersion from the explosion of artillery shell. Many substances perfectly stable under ordinary conditions will decompose under these circumstances.
The process for manufacture of a gas must be relatively cheap and simple. Practically all of the combat chemicals employed in the World War were previously known but were regarded merely as chemical curiosities. Methods of large- 335 scale production had to be devised and the necessary plants constructed from the beginning. It is a long step from the laboratory discovery of a promising new gas for war to the determination that it has all the required physical and physiological properties for field application; and it is another long step to its manufacture in large quantities. As an instance of the difficulties which may attend production, the Germans first fired mustard shells in July, 1917, but France was unable to retaliate until practically a year later while the British were 15 months in accomplishing this object.
As a consequence of these rigid technical and tactical requirements, only about 3,000 of the innumerable substances known to chemical science were considered during the war as possible combat gases. Of these only about 35 were found even suitable for trial in the field. From this group 11 were finally adopted and used widely as war gases; again of these not more than 6 were notably effective.
The Classification of the Chemical Warfare Agents
In any discussion of the chemical warfare agents the matter of classification is a basic consideration. There follows the present twofold classification of the Chemical Warfare Service of the Army based on physiological effects and tactical application. Additional gases could be included, but those here listed are generally considered as the most promising. There is always, of course, the possibility of emergence of new compounds of confidential nature.
(1) By Physiological effects.—
(a) Lung irritants.—Chlorine (CL), Phosgene (CG), Chlorpicrin (PS).
(b) Vesicants.—Mustard (HS), Lewisite (M-1), Ethyldichlorarsine (ED).
(c) Irritants.—
(1) Irritant smokes.—Diphenyl-chlorarsine (DA), Diphenyl-aminechlorarsine (DM).
(2) Lachrymators. —Chloraceto-phenone (CN), Tear Gas Solution (CNS).
(d) Incendiaries.—Thermite.
(2) By Tactical application.—
(a) Casualty agents: (CL)(CG)(PS)-(HS)(H-1)(ED).
(b) Harassing agents: (DA)(DM)-(CN)(CNS).
(c) Screening agents: (FS) (HC) (WP).
(d) Incendiary agents: Thermite.
A casualty agent is used to produce personnel casualties of such severity as to actually require evacuation. A harassing agent is used to force masking and thereby reduce the efficiency of the opposing forces; such casualties as result being of only brief duration. The specific purpose of employing screening and incendiary agents is self-evident from their designations, casualties to personnel being merely incidental. For this reason they do not fall strictly within the category of war gases and will therefore be omitted in the discussion to follow.
The factor of persistency should receive brief mention at this point, as being of extreme importance in naval tactical application. Persistency is the length of time that a gas remains effective at its point of release. If it remains in sufficient concentration to require protection of any kind at the end of 10 minutes, it is arbitrarily classed as persistent; otherwise as nonpersistent. Persistency naturally depends mainly upon the rate of evaporation of the agent, as modified by weather conditions and the character of terrain. Generally speaking, nonpersistent agents are true gases or smokes, and when released in the open tend to be rapidly carried away by wind or air currents. Persistent gases are ordinarily liquids and only slightly volatile. It may therefore be postulated that only persistent gases offer a possibility of effective naval attack by aircraft. However, a nonpersistent agent might have a casualty effect if released from a shell after penetration of a vessel.
The Lung Irritants
The first gases to appear in the late war were the lachrimators or tear gases. The lung irritants were the second group to make their appearance but were actually the first agents to wield an effective influence in war. In general, they are volatile compounds giving rise to nonpersistent gases on escaping from their containers. Chlorpicrin is an exception in that it is slightly persistent. The essential physiological effect of this group of gases is serious injury to the lung structure. This damage leads to a passage of fluids from the blood vessels into the tiny air sacs of the lungs, thereby interfering with the supply of oxygen to the blood stream. Death in lung irritant poisoning is analogous to asphyxiation by drowning, the water in which the casualty drowns being drawn into the lungs from his own blood vessels.
Chlorine was the first lung irritant to be introduced in the war and the dramatic story of the initial attack by the Germans at Ypres in April, 1915, has often been told. A cloud of 168 tons of chlorine from 5,730 cylinders was released over a front of nearly 5 miles against entirely unprotected troops. It extended for a distance of about 4 miles downwind producing 15,000 casualties of which 5,000 were fatal.
As the war progressed chlorine was used extensively for cloud gas attack but later on, when troops were equipped with gas masks, its casualty producing value was greatly reduced. It was also used in mixtures with other more toxic gases, such as phosgene and chlorpicrin, to promote the effective dispersion of these agents. However, as a combat gas chlorine is now chiefly of historic interest, there is little probability that it will be a factor in future warfare in view of the appearance of far more toxic lung irritants greatly superior in tactical application. Moreover, gas mask protection against it is particularly effective.
Phosgene was the most effective of the lung irritants in the war, in fact the outstanding lethal battle agent, 80 per cent of gas fatalities being due to this agent. A gas at ordinary temperature, it was projected m liquid form in enormous quantities in cylinders, artillery shells, trench mortars, bombs, and projector drums. It is about eleven times as poisonous as chlorine, and it is possible to build up a high enough concentration in the field so that one or two whiffs may be lethal within a few hours. It is a remarkable property of phosgene that the gas can be breathed without undue discomfort or coughing, which in the case of chlorine limits the intake, and it has a characteristically delayed action. Even a small intake varying in amount with the idiosyncrasies of persons is liable to cause alarming symptoms as long as 24 to 48 hours after exposure. Cases frequently occurred in the war of men who, not aware of symptoms at the time, declared positively that they had not breathed the gas, collapsing and dying after such long intervals.
Another peculiar aspect of phosgene was the so-called “tobacco reaction,” by which is meant that men who inhaled only very small amounts experienced an unpleasant flat taste on smoking cigarettes, often described as resembling hay. It may even be detected in the field by this reaction.
Chlorpicrin, commonly called the vomiting gas in view of its emetic action, is an oily liquid in the ordinary state and was used considerably in the war. It had a number of desirable offensive properties with a toxic effect somewhere between chlorine and phosgene. It was also a powerful lachrymator with the additional advantage of being capable of penetrating the German gas masks at the beginning of 1917. The main tactical idea in using this gas consisted in the fact that on penetrating the mask it produced an intolerable lachrymation, as well as coughing and vomiting, so that the enemy would be compelled to remove the gas mask and expose himself to the full concentration, as well as to the phosgene, which it was intended to disperse at the same time.
It has been previously found that the liquid stannic chloride which forms a smoke when atomized in the air had remarkable penetrative qualities. Stannic chloride is harmless in itself, but in order to increase still further the penetration of chlorpicrin, a small percentage (20 per cent) was mixed with it in all projectiles, artillery and trench mortar, used by the British Army. This mixture was known as NC and gradually replaced chlorpicrin, as such.
Chlorpicrin has a disadvantage in that it is readily decomposed by high explosive unless the bursting charge is specifically adjusted to the gas filling. With this precaution chlorpicrin was effective, but the fact that the present-day gas mask is adequately protective against it, and that more powerful and effective lethal agents are available, renders the future tactical employment of this gas questionable.
What may we venture to say as to the future of the lung irritants in war? These substances were the principal nonpersistent casualty agents of the war, and are the only agents known at present as suitable for use in the tactical offense when troops are required to occupy terrain within a few minutes after gassing. They therefore may be expected to play an important role in land gas warfare of the future. On the other hand these chemicals are not adapted for sea forces by reason of their nonpersistency, which will be further discussed in succeeding pages.
The Vesicants
The vesicants initiated a new principle in gas warfare in that they readily penetrated clothing, leather, rubber, etc., producing serious burns of any part of the body exposed. The vapor was highly dangerous when breathed and caused an intense inflammation of the eyes. The gas mask protects only the lungs, eyes, and face. Metaphorically speaking, the entire body requires armored protection against the vesicants. This means the provision of special protective clothing, shoes, and gloves.
It has been estimated that about 12,000 tons of vesicants were employed in battle in the war, mustard making up about 95 per cent of this total. Mustard was first introduced by the Germans on the Western Front in July, 1917, in the form of an artillery bombardment. This new phase of gas warfare maintained its dominant position for the remainder of the war. It was dispersed in both artillery and trench mortar shells. Depending upon the force of the explosion the liquid was scattered as a vapor cloud and a spray of liquid particles. The effect of personnel consisted of the direct action of the liquid spray and vapor cloud and the indirect result of the vaporizing of liquid mustard from the contaminated area.
Mustard is an oily liquid, the vapor having a faint odor suggestive of garlic, horseradish, or onions. With the unprotected individual, mustard vapor causes intense irritation of the eyes, air passages, and skin, followed by blistering of the latter and bronchopneumonia which is the usual cause of death. The vapor is three times as toxic as phosgene. The burns produced by the liquid mustard are similar to those from the vapor except that the course is more rapid and severe.
A marked characteristic is the delayed action, an interval of several hours elapsing before the development of blistering in contrast to a thermal or ordinary chemical burn in which there is no latent interval. A man can inhale a fatal dose of mustard vapor and yet not be aware of the exposure. Mustard has a very low mortality rate, but induces prolonged disability, whereas phosgene is primarily a lethal agent but the casualties are of short duration. The average mustard casualty in the American Expeditionary Force in France lost 60 days from the front.
Incident to this delayed action, mustard cannot be expected to inflict casualties during the progress of an attack and its persistency renders it impracticable for the attacking force to take ground which has been gassed until after a lapse of several days. It is particularly adapted to a retreating force or a force on the defensive. From the tactical viewpoint mustard is essentially a defensive war gas.
Lewisite.—After the advent of mustard it was soon realized that the ideal gas for the tactical offensive would be a nonpersistent or low persistent quick-acting vesicant, with a general poisonous effect on the system in addition to the vesicant action. With these objectives Lewisite was developed by the American forces but, although superior to mustard in some respects, the desired properties were only partially attained in the new gas. It was not placed in production in time for trial at the front.
Lewisite contains arsenic in the molecule. It produces burns similar in general to those of mustard from which arsenic can be absorbed, resulting in generalized arsenical poisoning. It is predicted on the basis of animal tests that 30 drops spread over the skin of a man of average weight would contain a fatal dose. Although much less persistent than mustard, it still falls in that category and, while less delayed in action, there is nevertheless a period of latency with respect to the skin. The vapor is almost immediately irritant to the breathing passages, and about four times as toxic as phosgene with absorption of arsenic through the lungs.
It penetrates materials similarly to mustard and therefore presents analogous problems of protection. A serious limitation of Lewisite for combat is that it is readily decomposed by water, one of the products being a less vesicant, nonvolatile solid. It would not be adapted to a wet, rainy region; the question as to whether or not this gas will be projected by future land or sea forces would seem to hinge primarily on the weather conditions to be considered in the theater of operations.
Ethyldichlorarsine.—Germany also called upon her chemists in the war period to explore the possibilities of production of a quick-acting nonpersistent vesicant for offensive operations where mustard prevented a follow-up of an attack. The answer was ethyldichlorarsine introduced in the spring of 1918. It was found to be about one-sixth as vesicant as mustard and, contrary to expectation, the great majority of the war casualties were of the lung irritant type; the vesicant action Proving to be secondary although considerable. The vapor was of about the same toxicity as phosgene but producing a violent irritant action upon the upper breathing passages resembling that of the irritant smokes about to be described. For the latter reason, if comparatively minute amounts are breathed before donning the gas mask, the resultant sneezing, coughing, and retching will force removal of the mask.
Ethyldichlorarsine is a gas of low persistency. Thus, the Germans found that terrain in summer could be safely entered in about one hour after gassing, while with mustard a delay of 48 hours or even longer was imposed depending upon weather conditions.
Prentiss expresses the opinion in his Chemicals in War that ethyldichlorarsine should be classed as a persistent lung irritant rather than a vesicant. He also points out that the gas presents so many valuable features that it will in all probability be given careful consideration in any estimate of chemical warfare of the future.
The miliary effectiveness of the lung irritants versus the vesicants in the war invites comparison. It is estimated that a total of 100,500 tons of lung irritants were expended causing about 876,853 casualties or an average of one casualty for every 230 pounds of gas. The majority of all gas fatalities were caused by this group. About 12,000 tons of vesicants producing 400,000 casualties were employed, mustard making up about 95 per cent of this total, with one casualty for every 60 pounds of vesicant or nearly four times the ratio for the lung irritants. Less than 10 per cent of all gas projected was in the form of vesicants, and yet the latter produced one-third of all gas casualties. This proportion would have been far greater if mustard had been adopted earlier in the war. The lung irritants were introduced in 1915 but mustard did not appear until over two years later. In fact it was projected by the Allies only during the last four months of the war.
The fatality rate for mustard was very low being only 2.5 per cent for the British Forces out of 160,970 casualties.
The vesicants unquestionably marked the outstanding gas development of the war and it is virtually certain that they will be relied upon in chemical tactics of armies of the future. In view of its high persistency and other characteristics mustard would appear to be the chief chemical threat to naval forces if the problem of successful projection upon enemy vessels can be solved and defensive measures neutralized.
The Irritants
By an irritant is meant a gas that irritates either the exterior or the interior of the body producing intense, though temporary, discomfort or even pain. The irritants are subdivided into the irritant smokes and the lachrymators.
(a) Irritant smokes.—These are solid, organic, arsenical compounds and were not dispersed as smokes in the war. DA, the first of this type, was introduced by the Germans almost simultaneously with mustard in what was termed the Blue Cross shell, the DA contained in a glass bottle being embedded in the high explosive. When scattered by the explosion it was liberated not in the form of a gas, but in fine particles. The enemy’s object was to penetrate the gas mask, causing such irritation as to compel personnel to remove their masks and expose themselves to other lethal gases dispersed at the same time.
In very minute amounts DA causes violent and prolonged sneezing with smarting of the eyes and lachrymation; in larger amounts intense burning in the nose and throat, terrific pain in the head and chest with a sense of suffocation and nausea. The pain in the head is described as like that when fresh water enters the nose when bathing but of excruciating degree. These symptoms are accompanied by the most appalling mental distress and depression, some cases becoming temporarily insane. However, the period of disability is short, the vast majority being returned to duty within a few hours and after-effects are rare.
The Germans fired millions of Blue Cross shells up to the end of the war but the casualties of the Allies were insignificant—hardly more than an occasional harassing effect, even though their gas masks were not proof against DA at first. This failure is explained by the fact that the compound was not sufficiently atomized by the high explosive to effectively penetrate the mask. A mechanical filter was eventually adopted as the principle of protection.
Subsequent studies by British and American chemists led to the finding that DA was vastly more effective in the field when released by heat in the form of an irritant smoke cloud. This is accounted for by the more minute size of the particles making up a thermogenerated particulate cloud as compared to the smallest particles resulting from the atomization of a solid. Unfortunately the Allies developed this new technique at too late a stage for use in battle. It was proved by field trials that under favorable weather conditions the German mask was easily penetrated at a distance of several miles. It was believed that such a smoke cloud attack on a vast scale to precede an infantry advance would have been highly successful.
DM was developed independently in the United States and Great Britain during this period but not in sufficient time to reach the front. It is the agent of choice as compared with DA for a number of reasons, the chief advantage being that large- scale production is much simpler and at lower cost. The so-called DM smoke candle of the Chemical Warfare Service consists of a metal can containing the agent and the heating mixture in separate compartments.
As to the probable military future of the irritant smokes, stress should be laid on their effectiveness as temporary casualty producers. On the other hand, all modern masks are equipped with special filters for holding back these smokes which in turn greatly increases the discomfort in breathing. It appears probable that they will play an important role in land warfare, but this does not hold for sea forces in view of the nonpersistency of these smoke clouds.
(b) Lachrymators.—Chloracetophenone (CN) is largely a post-war development, the agent being a white solid in the ordinary state. It can be effectively fired in high explosive shells but is much more efficacious in the form of a smoke cloud produced by the burning of 1 part of the agent and 3 parts of small-grained smokeless powder.
Tear gas solution (CNS) developed within recent years is a colorless liquid consisting of CN dissolved in a mixture of chlorpicrin and chloroform. It is classed as a persistent, remaining for 1 hour in the open in summer, and may be projected in artillery shell, mortar shell, and airplane spray and bombs. Like CN it sets up a piercing irritation of the eyes and profuse flow of tears, but in addition it tends to cause nausea and vomiting by virtue of the content of chlorpicrin.
The future status of lachrymators in war is uncertain. They present a decided advantage in the very low concentration necessary to force masking but they cause no real casualties. The irritant smokes are immensely superior as harassing gases in that severe though temporary effects are produced in unprotected personnel. It is doubtful if lachrymators will be utilized to any great extent by armies. For forces afloat present-day lachrymators appear to lack sufficient persistency to be effective except possibly in armor piercing shells.
Post-war Development
The principle of surprise in chemical warfare is of vital importance as in the use of other weapons. Various powers are conducting research to forestall any possible development by other countries of a gas that will penetrate the present gas mask, or otherwise overcome present means of gas defense. In view of the confidential status of such progress, we are not informed as to the production of new and more powerful agents since the World War. It is believed by certain leaders in chemical research that the probability of the discovery of new and more destructive gases is remote. The requisites of a war gas are so exacting that the mathematical probabilities are against it.
J. B. S. Haldane, the eminent British biochemist, states:
It is probable we have not completed the list of possible poisonous volatile compounds but I do not believe in the probability of anything very much worse than mustard for a very simple reason; in order that a chemical may have an appreciable vapor pressure, that is to say, that an appreciable amount of it may get into a given volume of air, it must have relatively small molecules. There are plenty of large molecules which have not yet been made, but large molecules do not volatilize and the number of small molecules which are at all likely to volatilize are already fairly well known.
Extensive post-war research has been carried forward by the principal nations to develop more effective technique of utilizing the successful World War agents, and more efficient means of anti-gas protection. The war ended leaving the problem of adequate defense against the vesicants mainly unsolved and this has been a point of concentrated attack. Great progress has been made along these various lines.
The chief post-war advance affecting technique and tactics is probably the development of methods of aero-chemical attack. It is rather remarkable that this phase of application was not introduced in the late war in view of the fact that it had extended to every other combat arm. This opens up far-reaching possibilities. By means of spraying persistent chemicals from aircraft, large bodies of troops can be covered or extensive areas can be made untenable in a short period of time and at any place in an enemy country. In land operations nonpersistent lethal gases may be put down effectively by means of chemical bombs under certain favorable circumstances.
For reasons pointed out in the preceding pages reputed discoveries of new and more toxic gases are regarded with mental reservations in research circles, and they usually refer to chemicals that have not passed beyond the laboratory stage or are deficient from the physiological, tactical, or economic standpoint. Still the possibility cannot be dismissed that more effective chemical agents may be produced. The development of an immediate-acting vesicant of the power of mustard but of slight persistency would be of immense tactical value for land forces. In a naval attack a quick-acting but persistent vesicant would be more advantageous.
Collective Protection against Gas at Sea
A consideration of this aspect of the subject must necessarily take into account the possible effects of gas at sea. This naturally raises the question as to the offensive status of gas versus that of high explosive. While gas is a recognized combat arm in land forces, it remains as supplementary to high explosive and is particularly applicable to certain tactical situations with respect to personnel casualties. In modern naval warfare the main objective is destruction of material and high explosive is unquestionably superior to chemical agents in this regard.
Certain limitations inherent in the properties of the war gases with respect to naval uses have already been mentioned. Nonpersistent gases would not appear to be a serious menace at sea. The dispersion of toxic gas or smoke clouds is mainly dependent upon weather conditions. Rain, high winds, a heavy sea or a dead calm would all be adverse. The length of time during which a ship under way would be exposed is likely to be brief. It appears that the effect of such gases would be chiefly harassing, that is, they would compel masking.
The possibility of gas shell penetrating into the working compartments of a ship releasing high concentrations of toxic gas in confined spaces must be considered. This would necessitate masking and therefore seriously hamper the efficiency of working parties in repairing the damage due to hits.
The most serious gas menace is the mustard spray or bomb projected by aircraft. Here we have to deal with liquid contamination of exposed personnel and of decks, hull, and superstructure, inclusive of material requiring frequent handling, such as exposed weapons, rigging, cables, boats, etc. If the outer envelope is incompletely sealed dangerous concentrations may invade the interior, especially if the gas collects in the vicinity of ventilation intakes.
The collective protection of the ship, as on land, is a defensive organization against gas which includes a system of gas sentries, gas alarms, and anti-gas personnel; the last named to be responsible for operating the ventilation system for the exclusion of gas from working compartments wherever possible and to the decontamination of the ship.
The importance of decontamination of material and personnel needs no emphasis as fighting efficiency will largely depend on the effectiveness of this procedure. A ship contains the living spaces of hundreds of men who are crowded in a small area with no possibility of leaving the vessel at sea, and with the hazard of carrying contamination from the active bridge or upper decks to the living quarters below. Decontamination from liquid vesicants will be a laborious and protracted procedure in view of the varied nature of the material exposed to such contamination. The procedure for personnel and their clothing would be based upon that practiced by land forces but would be complicated by many factors.
In conclusion, it is believed that gas, when utilized by naval forces, will be largely limited to persistent agents but only supplementary to high explosive. However, the projection of vesicants in some form appears to be practicable and there is no need to emphasize the imperative necessity of protective measures to meet it.
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