Flamethrowers - Encyclopedia




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"FLAMETHROWERS (Germ. Flammenwerfer). - The World War revived the old weapon of " liquid fire." No doubt, the use of incendiary projectiles and devices had never altogether vanished from modern warfare, but these have usually been employed for destruction of material rather than for effect on personnel, and we have to go back to the sieges of mediaeval times to find examples of the use of heat, as such, to repulse an enemy. The townspeople of a mediaeval city, having only massacre to expect if their walls were stormed, observed no limitations in their choice of weapons, and not only used incendiaries proper to destroy the besiegers' hoarding-work and catapults but also boiling oil against the bodies of the men. From time to time in modern history proposals have been made for flame-throwing devices, and one such was actually experimented with in Prussia about 1700. But until modern methods of storing a gas propellant under pressure came into being, anything in the nature of an effective flamethrower was impossible.

In reality therefore the flamethrower dates from experiments made in Germany a few years before the World War, when, no doubt in consequence of the trench warfare of Port Arthur, Richard Fiedler produced in 1906 a service model which was under experiment when the war broke out. Like other weapons of siegecraft this was brought into the field as soon as the nature of the fighting changed from open-field warfare to trench warfare. Already in the winter of 1914-5 they appeared sporadically on the western front, and they obtained their first striking success in the Bois d'Avocourt (Verdun) on Feb. 26 1915. It should be noted that the use of such weapons was not prohibited by the Hague Convention, save in so far as it might be called a weapon " calculated to cause unnecessary suffering " - a phrase which is susceptible of many interpretations. In this it differed from the gas warfare initiated at Ypres in April 1915, although by the accident of circumstances gas and flamethrowers have come to be associated in the popular mind.

When the German Flammenwerfer appeared it was considered essential both in France and in England to design weapons of this class at once; in England the question of their employment was reserved, but it was felt that the soldiers who were exposed to flame attack should, for reasons of moral, be made aware that similar devices were available on their own side. In France the military authorities proceeded without hesitation to the creation not only of the apparatus but of the units to work them. This difference in the way in which flamethrowers were regarded in the two chief Allied countries persisted to the end of the war. The French used them as constantly as the Germans, whereas in the British Army their employment on service was limited to a very few occasions in the battle of the Somme, and to the Zeebrugge attack of St. George's Day 1918. By the American Expeditionary Force they were not used at all, though the question of their employment was taken into consideration. In 1919 they figured largely in the local street-fighting by which the German Republic made good its authority.

The flamethrower essentially consists, in all designs, of (a) a container filled with some mixture of heavy and light oils; (b) a strong-walled vessel filled with air, nitrogen, CO 2, etc., under high pressure; and (c) a discharge tube with nozzle and in most cases an ignition device. Between (a) and (b) is a reducing valve, and between (b) and the nozzle a firing valve or trigger. When air or gas under high pressure is admitted into (a) from (b) it expels through (c) a powerful jet of oil, which when ignited (either at the nozzle or subsequently) becomes " liquid fire." Flamethrowers are essentially short-range weapons, whose characteristic effect is to make an area untenable by living beings, by actual burning and also by heating the surrounding air to an intolerable temperature. This effect imposes, as a condition of their use, maximum range, not only because range as such is a desirable military quality but because the operators themselves must not be put out of action by their own weapon. Range, however, is difficult to obtain with a liquid jet. Even in vacuo such a jet with an initial velocity of 50 metres per second would not theoretically range to 300 yd., and, owing to the resistance of the air, the maximum range ever known to have been attained in practice was 234 yd. actual throw (with an experimental British type of heavy flamethrower). Beyond the actual range of the jet there is of course an area (which varies according to the conditions of the shoot) made momentarily untenable owing to the heating of the air, and this area extends laterally as well as forward. But the fact of limited range remains a constant drawback. It is especially pronounced with the light portable types, few of which outrange the hand-grenade.

Amongst the design factors influencing initial velocity and therefore range, two are of principal importance, the pressure of the gas propellant in the oil container and the loss of energy in the discharger pipe and nozzle. The first would seem, at first sight, to be limited only by the weight and strength of the containers - those of the gas " bottle " in the first instance and those of the oil container secondarily. But in practice the size of the nozzle orifice sets an upper limit to working pressure; if it is too small in proportion to the pressure the liquid, instead of being propelled in a consistent jet, is atomized and loses its forward energy very soon. But the larger the orifice the greater the quantity of liquid discharged per unit time. Hence, to obtain a long throw of any useful duration the flamethrower must be large, heavy and cumbrous. Conversely, when minimal weight is important, either range or duration must be sacrificed. Up to the limit 'thus fixed, of course, maximal pressure is aimed at in design, and it is found that, with modern materials and workmanship, gas bottles capable of standing the unreduced or storage pressure and oil containers able to endure the reduced or working pressure can be constructed within practicable weights.

The second important factor is loss of head, which varies with the length and smoothness of the internal surface of the discharge system, and is affected still more by the occurrence of abrupt bends and contractions in the piping or nozzle. A discharge system as straight, as short, and as large in bore as possible is therefore aimed at. But here again practical limits exist. In all heavy and medium and in most " knapsack " flamethrowers the position of the container has no relation to the axis of the jet. It is not, like a gun, pointed in the direction of the target, but is built in under cover or stood up on the ground or carried on a man's back, and aim is taken by pointing the nozzle only. Hence the most that can be done is to smooth out the angles of bend as much as possible and to diminish the length of piping to the strict minimum. Large bore is always desirable but not always attainable, since increased volume of oil per unit time means either increased dimensions for the oil container or diminished duration of action without reloading.

The dimensions of the nozzle itself, in this connexion, are important as affecting the form of the jet. Progressively, in its passage through the air, the solid vein of liquid breaks up into globules and loses its forward energy; the higher the initial velocity the longer this break-up is delayed, and velocity is, as we have seen, a function of working pressure and orifice dimensions. Moreover, the larger the vein itself the less surface it presents to disintegration by the air for a given volume; and the same reasoning excludes all crosssections of the nozzle other than circular.

The oils employed varied, in the World War, according to available supplies, but were always in principle mixtures of heavy oil and light oil (petrol or benzol), the former for the sake of maintaining forward energy in the air (giving " sectional density " in ballistic language), the latter for ease of ignition. In winter the proportion of light oil was increased up to one-third in the French service.

The propellant gases used were also varied. Compressed air, being most readily available, was probably the most frequently employed. The Germans even tried compressed oxygen, a most dangerous expedient when nozzle-ignition is employed, as the mixture in the interior of the container is liable to detonate if a back flame from the jet reaches it.' This risk attaches also in a lesser degree to compressed air, and inert gases are always preferable.

CO, has the disadvantage that it forms a deposit in the piping and so increases loss of head, and in the end nitrogen - either the pure product of chemical factories or a " deoxygenated air " produced in the field by a mobile plant - was generally accepted.

So far only the expulsion of the oil jet has been considered. Broadly, there are two forms of ignition. In the one the ground occupied by the enemy is sprayed with the unignited oil, and then fired by throwing on to it incendiary bombs or grenades. This is mechanically the simplest way, and it gives the most thorough effect, since all parts of the ground, even the floors of trenches, are set on fire. But the throwing of grenades on to the correct spot is a difficult 1 A very serious accident occurred on one occasion in England from this cause, an oxygen bottle having been accidentally sub.. stituted for an air bottle.

matter, especially with the long-range heavy flamethrowers, and surprise effect - which, in the opinion of some, is the principal if not the only asset of the weapon - is entirely lost. The other method is to fix an igniter to the nozzle; this fires the jet at the outset, ensures surprise and moral effect, for the liquid-fire jet, with its roar, its heat, and heavy smoke intermingled with darting masses of flame, is a terrifying thing. On the other hand nozzle-ignition presents very difficult problems which have never been satisfactorily solved, and the actual burning effect is more local than is the case with the simpler method. On the whole nozzle ignition is to be preferred whenever a reasonably certain ignition device is available. The French made use of both methods, the Germans and British exclusively, or almost exclusively, of nozzle ignition. It was at one time supposed that the unignited jet ranged farther than the flaming jet, but this is not proved. French experiments indicate that what is lost in " sectional density " by igniting the jet is regained by the fact that the surrounding air, heated to a high temperature, offers a lessened resistance.

Ignition devices may be simple portfires (or even petrol-soaked wads) attached by hand to the nozzle and ignited before aim is taken, or more elaborate electrical and mechanical devices. In all cases they are required to ignite, not the oil itself, which emerges in too rigid a column to respond to the spark, but the film of petrol vapour which forms round the column. The spark must be emitted by the igniter as close as possible to the emerging jet without actually touching it. Moreover it must be protected against the wind. Further, the igniter must remain alight and in the correct position during the duration of the throw; this condition is very difficult to satisfy in the case of portable flamethrowers which operate by a succession of short, sharp jets controlled by a trigger, save by the clumsy expedient of a long-burning portfire. Amongst the many forms of ignition three may be specially mentioned: (a) A British pattern in which two sparking-plugs were mounted in a cup containing petrol, and fired by a magneto generator.

(b) A French type, giving the very long burning required for the successive shots of the portable flamethrowers by means of a tubular magazine fixed to the nozzle. In this magazine was a long stick of alumino-thermic composition, which was continually urged forward by a spring as its head burned away. Primary ignition of the portfire itself was by means of a cerium-steel " briquet." (c) The German service igniter (fig. i), which was very ingeniously devised and was based on inertia. It was a double-walled cylinder attached to the nozzle-tube. The space between the inner and outer walls was filled with an alumino-thermic composition, open to the air at the top. Inside the hollow of the cylinder and in prolongation of the bore of the nozzle-tube were a piston, a spring, a strikerneedle mounted on a pellet, and a cap with powder-relay. Between the cap and the striker-needle was a fixed disc of cardboard. On release the sudden impact of the jet on the piston compressed the spring and the striker against the cardboard disc, then after a moment the needle penetrated this disc, and the spring, decompressing itself, forced it on to the cap and so fired the powder relay that ignited the composition. The attachments which secured the striker, etc., in the bore of the cylinder were instantly burned through, and the jet, blowing out these obstructions, issued and was ignited by the burning composition as it emerged.

The t y pes of flamethrower designed by the three belligerents were classified broadly as heavy, medium or semi-portable, and portable. Those of the heavy class, built for range, all required fixed installations; medium types were simply smaller editions of the heavy types, kept down in weight so as to be able to follow up an advance without undue difficulty; while the portable weapons were without exception designed for use in the course of the attack itself, and especially for the " mopping-up " of captured trenches and for securing the flanks of a line of trenches during " consolidation." In reality, therefore, there are only two types, the heavy and the light, and these are technically very different.

Heavy Flamethrowers

Of the various types of heavy flamethrower which were evolved in the war, the British show both the best ranging power and also perhaps the greatest variety, this latter being due to the fact that, officially, they never passed beyond the experimental stage into that of a " service store." The first model to be tried was that designed by an American, Joseph Menchen, which was put before the War Office in March 1 9 15. This was a very large apparatus, several containers being coupled up in series to a single pipe and nozzle, the latter being aimed from under cover by means of power derived from a bypass on the air bottle (a complication subsequently abandoned). The intention of the branch of the War Office concerned (which subsequently became the Trench Warfare Department of the Ministry of Munitions) was to employ the apparatus not in trenches, for which it was evidently too cumbrous, but to mount it in a large armoured vehicle of the caterpillar class. Such a vehicle was built, concurrently with the first tanks but on a larger scale so as to be able to carry a big supply of oil for the flamethrower, which in the Menchen design had a range of 100 yards. This idea of the flamethrower-tank was, however, allowed to drop owing to a variety of causes, of which the principal. were the dislike of the British G.H.Q. in France for flamethrowers generally, and the concentration of caterpillar-building resources at home on the gun-carrying tank. Experiment proceeded therefore on heavy types intended for trench warfare, and greater lightness and simplicity than was possible with the Menchen design was aimed at. Later in 1915 the Department produced a heavy flamethrower " battery " which embodied many of the features of the Menchen, and some of those of the Hersent apparatus which had been evolved in France. This " battery " is typical of the normal heavy flame-thrower.

The " battery " (fig. 2) consisted of four vertical cylinders 16 in. in diameter and 48 in. high; on the top of each cylinder was a valve (controlled at first by a wheel and later by special mechanism) which was attached to a siphon tube in the interior of the container. The four valves were connected up in series by short lengths of flexible metallic tubing. The container communicated by a length of flexible tube with a rigid tube terminating in a nozzle; this discharge tube was mounted in the trench parapet behind a shield in such a way that the jet could be delivered in any direction and with any elevation. In the final container valve i.e. that leading to the delivery piping - was mounted a trigger valve. On each container was strapped a gas bottle (compressed air, later nitrogen) containing 60 cub. ft. of gas compressed to i,800 lb. per sq. inch. Between Fasteners Cap Cardboard Disc Striker Pellet Spring Composition Piston this and the oil container were interposed a reducing valve (to reduce the storage pressure to a working pressure of 250 lb. per sq. in.) and a pressure gauge. Each oil container, when filled about threequarters full (as was the usual practice), held 25 gal. and weighed 180 lb. filled. Ignition was at the nozzle by means of the electric device above mentioned. The range of this model was about 90 yd. actual throw. This apparatus, modified in details, was operated on one or two occasions in very unsuitable conditions during the battle of the Somme 1916, and was then rejected by G.H.Q. 1 But before experiment was abandoned two important alterations were made. (a) The valves between the separate containers were done away with, and the freer flow of oil thereby obtained enabled a " record " range of 134 yd. to be reached. (b) The " director tube " built into the parapet was replaced by a so-called " monitor," a lazy-tongs device carrying a short, universal-jointed, nozzle-tube, which was raised above the parapet only during firing, the whole installation at other times being below ground in a dugout. Other improvements were made to facilitate assembly and taking down in trench conditions. On one occasion a complete " battery " of four containers and monitor was taken down, removed, reassembled, filled and fired in slightly less than 15 minutes by ten men. The container unit was also lightened.

French heavy flamethrowers were substantially of the same character as the British model just described, but simpler. They did not range quite so well. Storage pressure was somewhat higher, working pressure slightly lower than in the British engines. The unit container was shorter and wider, and of lower capacity; the " battery " usually consisted of three containers placed one behind the other and connected by coupling-pipes at an acute angle to a single collector-tube which carried the nozzle. As above mentioned nozzle ignition and ground ignition were both used.

The German Grof (grosser Flammenwerfer) was similar in capacity to the British " battery " type, but otherwise resembled the French.

A heavy flamethrower of an entirely different type was the Livens, designed by Capt. Livens, R.E. In this the containers were, so to speak, elongated until they took the form of a single long 9-inch pipe stowed horizontally in a deep dugout or gallery. In the pipe worked a floating piston which separated the gas and the oil positively. Along this pipe, at intervals, were placed refilling tanks, so arranged that at the conclusion of each shoot the pipe-container could be refilled with oil very quickly by power supplied from the main reservoir of propellant gas. In the model here described three shoots could be made, each of 80 gal., in four minutes. The propellant gas, stored in the usual bottles, was admitted to a welded reservoir which was tested to 1,800 lb. per sq. inch. This equalizing reservoir gave a powerful and steady drive at the relatively high working pressure of 325 lb. per sq. inch. At the end of the container pipe was a " monitor " or rising discharger, arranged on the principle of a hydraulic ram, worked by the oil itself. This rose through a hole in the roof of the dug-out, delivered its shot, and sank automatically when the oil which supported it was drained off below.

Portable Flamethrowers

These were used to a far greater extent in the World War than were the heavier types. In most cases the container with the gas bottle strapped to it was carried on the man's back, and the discharger tube with nozzle carried in his hand, the two being connected by the usual flexible pipe. The necessary lightness was obtained of course by the sacrifice of ranging power, both quantity of oil and working pressure being lower (3 gal., and 140 -170 lb. per sq. in. respectively in the French " Schilt " types) .

The general principles were similar to those of the heavy flamethrowers, except in the method of release. Whereas in the heavy types a single long-ranging shot of great power is fired in one blast, in the light type or at least in those light types designed after the requirement had been realized - a succession of very short spurts is arranged for by a quick-acting trigger-valve of some sort. This enables the user to move hither and thither, driving back now one party of the enemy, now another, or clearing several dugouts in succession without reloading. In earlier French patterns ignition was by incendiary grenades after a shot of unignited oil, but the tactical usefulness of this weapon, even more than that of the heavy type, suffers by this limitation, and in all later French models nozzleignition is fitted. Of these the Schilt " No. 3 bis " may be taken as representative (fig. 3). Its outstanding characteristic is the power of delivering very many short shots without reloading. The " record " is no less than 103, but such a figure can only be obtained at the expense of range, and the usual practice was to use up one filling in about 8 or 10 shots with a range of rather less than 30 metres. The ignition device is the " tubular magazine " mentioned earlier and burns for 8-9 minutes. The dimensions are: container 2 cm. thick, 55 cm. high and 20 cm. in diameter, tested to 427 lb. per sq. in. with a capacity 3 gallons. The gas is at a storage pressure of 2,133 lb.

1 The available sets were handed over to Russia, a company of escaped Russian prisoners of war being formed and trained in England to handle them. No use was apparently made either of the apparatus or the trained men, owing to the Revolution.

per sq. in., which a reducing valve converts to a working pressure 171 lb. per sq. inch. The trigger valve has to be held down in operation and instantly springs up and closes the passage of oil if the operator is shot - an important point, as experience had shown in the case of the earlier small flamethrowers, which emptied them FIG. 3.

selves in a single shot. A tap is also fitted, at the origin of the flexible tube, which is turned on in going into action. The flexible tube is about 2 ft. long, and 4 in. in bore, the nozzle pipe also 2 ft. long with an orifice of 3 2 inch. The total weight, full, is about 65 lb. Fig. 3 shows the apparatus in action. Like all French flamethrowers it was designed by Capt. Schilt of the Paris sapeurs-pompiers, who also organized the special flamethrower companies named after him.

The original German light Flammenwerfer, known as Kleif, was a 3-gallon en g ine which presents no particular point of interest. It was replaced by a smaller weapon known as Wex, which had a capacity of 24 gal. and was fitted for successive shots. Both " Kleif " and " Wex" were operated by two men, one carrying the container knapsack-fashion while the other carried the discharge pipe and moved about as required.

The early British types known as the Norris, or Norris-Menchen, were of much the same general design as the Schilts; the first emptied themselves at one shot, the later ones had trigger valves. Another type, invented by Lt. Lawrence, R.E., and originally designed to throw either poison-gas or flame or both, was, after modification to convert it into a flamethrower pure and simple, found to possess a much longer range, as well as a better balance of the elements of the design than any existing model. Its range was no less than 45 yd., and it was capable of maintaining that range for some 15 to 18 shots from a single filling of 3 gallons. Safety was ensured by the use of inert gas and by the fact that if the operator lost control all valves automatically closed. This type was under manufacture in Russia in 1917 at the time of the Revolution. Experiments were also made in England with smaller models, some of which were used in the Zeebrugge landing in 1918. Finally, a flame projector was designed but never actually used, which acted in the same way as a land mine, i.e. it was buried and left to itself, inert, till the enemy in his advance stumbled upon a tripwire which set the machine in operation.

Tactical Uses. - Flamethrowers used in the World War were in all the three countries which employed them engineer weapons. In Great Britain those used on service were manned by a unit of the Special Brigade R.E. In France Capt. Schilt, the designer of the Schilt throwers in use, organized some seven companies of engineers known as compagnies Schilt for flamethrower work. In Germany it was the special province of a unit of pioneers which from small beginnings finally became the Guard Reserve Pioneer regiment, and lent its weapons and its men to the " assault battalions " as required. These battalions generally included in their attack formations a number of portable " Kleifs " or " Wexs." The G.R.P.R. also found heavy machines (two-coupled) and personnel for shell-hole warfare and anti-tank defence.

In reviewing, even generally, their tactical work in the war, and estimating their future potentialities, it is obvious that a clear distinction must be drawn between the heavy and the light types. The intermediates were, and so far as can be seen will' always be, an unnecessary type possessing the defects without the virtues of the others.

Too little use was made in the war of true heavy types, such as the British " battery " and " Livens," for any final judgment to be passed on their usefulness. But it is evident that that usefulness will be confined to siege warfare, so far as ground installations are concerned. Quite apart from the necessity of burying the whole apparatus in shell-proof dugouts, the difficulty of supplying it with oil for constant use is considerable: eighty gallons of mixture with a specific gravity of 8-the contents of a Livens tube weigh 640 lb. without the transport receptacle, and three shots can be fired in four minutes. Stated in this way the problem is the same as that of supplying an II-in. howitzer emplaced in the foremost trench. The load can be brought up in smaller units, it is true, whereas a shell cannot be subdivided for transport. But it is nine times as bulky, and continuous supply would be as difficult in the one case as in the other. Another consideration is the material itself-in some conditions of warfare petrol and oil may be more precious than iron and steel. Thirty " Livens " machines on one mile of front would consume about I,000 gal. of petrol (neglecting the oil) per minute of actual continued activity. Fifty-five minutes of this activity on one mile of front would consume as much essence as the whole fleet of lorries belonging to the French Army consumed in a day during the winter of 1917-8. Evidently then the heavy flame projector if used at all will only be used in situations and tasks for which no more economical and handy weapon is available. The question is-do such situations exist? And the answer is evidently that, even if they do exist, they are not found on any considerable frontage at the same time. And so we find that the utility of the immobile heavy flamethrower is restricted to certain points and certain circumstances, such as may here and there be found (but not necessarily foreseen) in siege warfare. Any future that the heavy flame projector may possess in field warfare, or even in large-scale trench warfare, then, will depend on its being made mobile, i.e. on its being mounted in a tank.

The portable flamethrower, on the contrary, found many occasions of useful employment in varied conditions during the World War. Amongst its roles were: surprise attack following a stealthy approach, to enable an infantry attack to debouch from trenches; " mopping-up," i.e. clearing a captured trench system of isolated but still dangerous parties of the enemy while the main attack presses on; blocking the flanks of a captured length of trench; forcing the surrender of enemy parties which have taken refuge in dugouts (perhaps the most frequent, if not the principal role in trench-warfare offensives); holding off close attack upon a party withdrawing, e.g. after a raid; engaging a strong point frontally while infantry work round the flanks. This catalogue shows the variety of functions which may be and have been carried out by small flamethrowers. It will be noticed that many of these roles are by no means peculiar to trench warfare, and also that nearly all presuppose close cooperation with small bodies of infantry, the tactical units of the future. It is too much to say that the flamethrower is indispensable in the performance of the average battle task of modern infantry, but it is, on occasion, undeniably more useful than other close-range auxiliaries of the infantryman. Its main handicap is the difficulty of maintaining oil supply in an advance of great depth. This is serious, and may restrict it to employment in the methodical attack and defence of fortified regions. (C. F. A.)

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