Ensuring the secrecy of objects in the conduct of armed conflicts of varying intensity, as an important aspect of their protection: history, status, development of the process

Introduction

Within the framework of the historical confrontation between the means of attack and defense, methods of protection have developed and are developing in two directions: both in terms of ensuring the physical security of objects, and increasing their secrecy, countering enemy reconnaissance and aiming. At the present stage of this confrontation, with an increase in the range and accuracy of the means of destruction, the second direction becomes a higher priority. Mathematical calculations show: based on the fact that the radius of the striking effect of the munition decreases in proportion to the cubic root of the square of the distance, in order to reduce the probability of destroying objects, it is more effective to ensure a miss of the ammunition used on them, which varies according to the normal law, than to strengthen the protection of objects by increasing, for example, the thickness of armor (Figure 1).

Figure 1. Assessment of the effect of a miss on the probability of damage to the shelled object under the normal law of deviation distribution

This approach is especially relevant for the case of using high-precision ammunition with homing systems, when a miss is ensured by countering reconnaissance, targeting and guidance systems. Counteraction to these systems is implemented, first of all, through the improvement of camouflage means in the appropriate ranges. The historical retrospective of the described process can be clearly seen in the development of means of ensuring secrecy in the optical range.

As part of this retrospective, it can be recalled that in the early stages of the development of military art, during the conduct of hostilities, units of the warring armies used special, distinguishable from afar, elements of visualization of the situation: distinctive badges of legions, pennants, banners, details of uniforms, for example, colored plumes on helmets. With the increase in the scale of the battlefield, more effective measures were required: the introduction of colored versions of military uniforms and even horse suits for different regiments, providing visible differences between units, both of the opposing armies, and within each of them at a considerable distance. Color differentiation became possible with the advent of regular armies, and, according to historical data, the primacy in the implementation of this approach can be considered to belong to our country – for the first time, an intentional color difference appeared in the uniforms of the Streltsy regiments back under Ivan the Terrible, during the military reform of 1549-1560. The need for such solutions for the color separation of the uniform was determined by the method of combat operations management, in which the assessment of the current situation was carried out visually ^[1]. At the same time, European armies, consisting mainly of mercenary units, still fought in ordinary clothes, distinguishing opponents only by colored ribbons on uniforms and hats. With this in mind, according to one version, the word "gang" in many European languages came from the German das B a nd (ribbon): from the colored ribbons that the mercenary combat groups used to designate themselves at that time. The color differentiation of field uniforms appeared in European armies only at the beginning of the XVII century.

With the development of science and technology, the advent of effective long–range and rapid-fire weapons, in accordance with the laws of dialectics, the principles of military art were improved - the scale of hostilities, their spatial and quantitative indicators increased. The combination of these factors led to a change in the identification functions implemented by the military uniform in favor of increased secrecy. With the development of weapons, the importance of camouflage only grew: with the advent of aviation, it was necessary to disguise from above, as well as at a previously safe distance from the line of contact of troops. With the development of radio communications, masking on the air was required, and as the battlefield became more informatized, it became necessary in the information space. Measures to ensure secrecy began to be divided into tactical, carried out within the framework of the engineering support system on the battlefield, and strategic, carried out at a higher level.

Currently, with the development of robotic means of conducting armed struggle, with the spread of hostilities into different physical environments and virtual space within the framework of the concept of multidimensional actions (Multidomain battle, MDB), new challenges have appeared, both in terms of ranges and environments of camouflage, and in its fullness.

But all these changes do not reduce the importance of measures to ensure secrecy in the visible part of the optical range, implemented both by bringing the color of items of clothing, equipment and military equipment to the background of the surrounding area, and by optical and physical distortion of the contours of objects ^[2].

1.Materials and methods used

The main research methods used are analysis and synthesis. Based on the analysis of the features of previously used and currently existing methods of ensuring secrecy, a forecast for possible directions of their development is synthesized.  The use of a systematic approach that takes into account disguise as part of the engineering support of combat operations made it possible to consider these issues comprehensively.

As a limitation, it is accepted that the research is conducted in the field of tactical camouflage, in terms of ensuring the secrecy of objects, without addressing the issues of disinformation and misleading the enemy, used at higher levels of action. The article mainly deals with the use of camouflage schemes of uniforms and coloring of equipment to distort the visual characteristics of objects.

The source base of the research was made up of scientific and historical, managerial, organizational and technical documents that are in the public domain.

2. General historical analysis on the subject of the issue

Field military uniforms began to be sewn from protective fabric in the late XIX – early XX century. For the first time, the khaki uniform (English - khaki, from the Persian "haq" - dusty) was used by the British army in India in 1867-1868 to provide support units. By the beginning of the Anglo-Boer War of 1899-1902, the main units of the British army had already been transferred to a new field uniform, replacing the red coats, which ensured a reduction in losses from small arms, the rate of fire, range and accuracy of which had increased significantly by that time. Protective uniforms proved themselves well on the battlefield, but neglecting the use of optical camouflage in the era of rapid-fire and long-range weapons was expensive for troops. Russian Russian infantry, dressed in white tunics, suffered high losses from small arms during the Russo-Japanese War. The literature describes cases when our soldiers specially put on old tunics that had lost their whiteness before the battle, which in some cases was regulated by the instructions of the command ^[3]. Taking into account the experience of combat operations, before the First World War, the uniform of the protective color was adopted for the supply of most armies.

But simply approximating the color of the masked object to the color of the surrounding area did not fully solve the problem of countering the detection and recognition of objects by the enemy. The way out, as it happens, was suggested by nature – a complex coloring that blurs the contours of the object, hiding its geometric center, individual details and direction of movement in order to make it difficult to assess the type and nature of the actions of the observed object. It is considered to be the beginning of work on such coloring in 1909, when the American artist Abbott Handerson Thayer published the book "Concealing Coloring in Animal Kingdom", which described the methods of ensuring secrecy used in nature. And in 1939, the French artist of Russian origin Vladimir Baranov-Rossine patented a spotted military uniform ("pointillistic dynamic camouflage") or "chameleon method" ^[4]. Anyway, the very concept of "camouflage" appeared in Russian and many other languages from French camouflage. The principles of masking proposed by experts did not just bring the color of the object closer to the background of the terrain, they provided blurring of the contours of objects, hiding their type, geometric center and direction of movement, implementing a fundamentally new approach to increasing stealth.

However, it is possible to talk about any priority in terms of the invention of camouflage quite conditionally: work on the creation of camouflage uniforms was carried out simultaneously with France in Germany, where a "splinter" (German Splittertarnmuster) or "colorful" camouflage (German Buntfarbenmuster) was developed, in Italy (Italian M1929 Telo mimetico), in other countries.

By the beginning of World War II, camouflage was used in all the leading armies of the world, but not massively, but in the form of capes and camouflage suits used by specialists solving certain important tasks: scouts, snipers, sappers. The schemes of army camouflage patterns were developed for the specific type of terrain on which it was supposed to conduct military operations. The characteristics of human vision in the daytime were taken as indicators and criteria that determine the detail and color saturation of a drawing, its geometric structure and contrast. Camouflage was created both taking into account the geographical features of the area of the intended battle, and seasonal natural changes. For example, winter camouflage has been used quite actively since the Second World War and up to the present time – white masks and suits worn over the main uniform. These suits come in both plain white and two- or three-color spotted coloration, similar to the German Schneetarn^[5].

In the Red Army, camouflage uniforms were adopted for supply in the first half of the Great Patriotic War for snipers, sappers and scouts (Figure 2). At first, they were hooded camouflage robes worn over the main uniform. Where, in fact, did the word "camouflage" used in Russian to describe any camouflage suit come from. Later, camouflage robes were replaced with more practical suits consisting of jackets and trousers, also worn over the main uniform and made of the same fabric as the masks, with a pattern of uneven spots (in the shape of an amoeba) in brown or black, applied on a basic khaki or green background. The official name of such a scheme is "deforming coloring of the 1935 sample". In 1942, camouflage suits of light green color with leaf-shaped patterns appeared (the "deciduous forest" coloring), and in 1944 – the "palm" type coloring of four types ^[2].

Figure 2. Camouflage suits of the Red Army in the colors "deciduous forest" and "amoeba" on the participants of the historical reconstruction club "Iskra" (photo by the author)

During the same period, the use of camouflage uniforms was also carried out by the Allies. So, in the US Army, camouflage was used in the European Theater of Operations, which served as the prototype of a later version of Woodland – a pattern with irregularly shaped spots of four colors. In the Pacific Theater of Operations, US Marine Corps personnel used the US pacific camouflage, which was a basic khaki base, on which patches of green, light and dark brown colors were applied. Camouflage suits were made double-sided, with different color options on different sides of the fabric, which allowed them to be used in operations in areas with different soil and vegetation ^[2].

With the development of the chemical and textile industries, the cost of complex fabric coloring has decreased and it has become possible to mass produce uniforms directly from camouflage material.

On the one hand, this has generated a number of positive factors:

- the range of supplies has decreased;

- camouflage uniforms are more convenient to use than camouflage suits;

- the use of camouflage has been made widespread.

An example of the use of such uniforms: Denison smock jackets used during the war in the British army with a "smear" type coloring. The pattern of the jacket fabric included a combination of spots and smears of sand, green, brown and black colors, similar to the pattern of modern DPM (Disruptive Pattern Material) camouflage, but of a larger size.

On the other hand, the use of camouflage uniforms also had some limitations. If the Theater of operations itself is not changed often, then the change of seasons is an objective factor affecting the disguise. It is not always economically feasible to change uniforms for each season, so it is easier to use camouflage capes and robes. In addition, ordinary uniforms do not have some factors of specialized costumes, they distort the physical contours of objects less. Therefore, both then and now, camouflage suits or capes are used for winter conditions or for personnel solving special tasks in which secrecy is more important than convenience.

Returning to the period under consideration – in the German army, back in 1931, the Zeltbahn-31 camouflage cape appeared, implementing a "splintered" pattern (German Splittertarnmuster). During the Second World War, after experimenting with sharp–angled "splintered", "schrich" and "deciduous" colors, the Wehrmacht (Wehrmacht) developed a fairly effective camouflage coloring "Flectarn" (Flecktarn, from the German der Fleckt – "spot, blot" and die Tarnung - "disguise"). "Flectarn" is a three-, four-, five- or six-color "explosive" camouflage coloring. The use of groups of multicolored dots created an optical noise effect, eliminating clear boundaries between different colors and blurring the contours of the masked object. In total, by the end of 1944, the Wehrmacht used up to forty variants of camouflage colors, implementing mainly Flecktarn variants: Platanenmuster, Rauchtarnmuster, Palmenmuster, Sumpftarnmuster, Eichenlaubmuster, Erbsenmuster, Leibermuster and the like (Figure 3).

As in Britain, in Germany, not only camouflage capes and suits were developed on the basis of the flectarn coloring, but field uniforms were created, used mainly in field units of the SS (die Waffen-SS). The latter formed a certain negative attitude towards the rather successful "flectarn" coloring method – after the war it was forgotten for a long time, returning to use only in the late 1970s ^[2].

Figure 3. Variants of camouflage coloring of Wehrmacht uniforms (collage by the author)

The allies of the Germans also had their own developments in terms of camouflage, implemented mainly in the form of army capes, such as, for example, the Italian tent tent (it. telo tenda) in the M1929 Telo mimetico coloring.

3. The development of camouflage in the post-war years

The experience of the Second World War showed the high importance of all aspects of disguising personnel, equipment and facilities. It is logical that the development of camouflage methods and the improvement of camouflage colors for field uniforms continued. An example is the content of guidance documents developed in the US Armed Forces, such as the charter FM 5-20 "Concealment, basic principles", FM 5-20A "Concealment of personnel and weapons", FM 5-20B "Concealment of military equipment", FM 5-20G "Concealment of areas of deployment of rear facilities and equipment fortifications", FM 5-20H "Means and techniques of concealment" and a number of others.

Taking into account the provisions of these documents, the armies of the leading NATO countries have developed a large number of camouflage options: ACUPAT- Army Combat Uniform Pattern, MARPAT - Marine Pattern, DPM - Disruptive Pattern Material, MTP - Multi-Terrain-Pattern, CCE camo-Camouflage Central European, Flecktarn, Tropentarn and others (Figure 4, 5).

Most of the colors include variations for different theaters of war and/or seasons: vegetation, desert, urban colors, winter and others. The variety ensures that the basic set of colors is as close as possible to the coloring of the terrain on which it is supposed to conduct combat operations. After all, studies have shown that poorly chosen camouflage colors lose out in providing concealment to a uniform color close to the background of the area. Therefore, in order to increase the effectiveness of camouflage, sets of uniform colors should, in an average form, correspond to the soil and vegetation of the theater of military operations.

Figure 4. Variants of camouflage of NATO countries: Woodland, ACUPAT, MARPAT, Fecktarn (collage by the author)

Figure 5. Variants of the desert camouflage of NATO countries: DPM Desert of the British army, six-color desert of the USA, ACUPAT, Tropentarn (collage by the author)

Work on improving camouflage colors was carried out in the USSR army, and then in Russia. In the Soviet Union, the "silver leaf" pattern of the 1957 sample was developed for camouflage overalls (the official name is "Coloring of the 1957 model, the "Silver Leaf" variant, aka "Birch", KLMK suit), the basic camouflage for the field uniform "Butan/Dubok" of 1984, which existed in the form of color solutions for forests and for desert-steppe areas. A special KZS suit had a coloring similar to the "birch tree", only in a different color scheme. This mesh suit, in addition to optical camouflage, provided protection from the light radiation of a nuclear explosion due to a special impregnation that forms a haze when exposed to intense light radiation ^[6].

The armies of the Warsaw Pact countries used their own camouflage variants, most of which were formed on the basis of the German "needle" coloring (German Strichtarn) with different variations, such as additional spots or transverse strokes. The exception was the uniform of the Hungarian army, which had a specific coloring of the "tereptark" M49/82.

The first variants of camouflage of the Russian army: The HRV-93 and HRV-98 Flora were created using Soviet developments. Subsequently, a completely new camouflage pattern was developed – "Digital Flora", which reduces the level of visibility of military personnel, especially for electronic-optical surveillance equipment (official name "Uniform camouflage coloring + color code / variant").

Although it is not entirely correct to talk about the "official" names of camouflage – the names of the types of colors are used in special documents and during R&D, and the camouflage form itself differs only by articles from the nomenclature of the clothing service ^[5].

However, reducing the visibility of personnel is realized not only by coloring field uniforms and camouflage suits, but also by other methods: camouflage capes, removable covers for equipment items (pouches, backpacks), face and hand makeup, camouflage ribbons for wrapping weapon elements. The use of interchangeable elements allows you to bring the color of the camouflage as close as possible to the area where the military personnel are currently operating. These components can be endowed with additional useful properties, for example, water resistance (Figure 6). And besides, the interchangeable component approach has additional useful applications. For example, army bowlers in the Soviet army were painted with protective enamel, and aluminum landing kits were not painted, they were carried in a protective cloth cover. As a result, after the first cooking over a campfire, the paint of the army pot burned and difficulties arose in bringing it to its original appearance. And the bowler hat from the landing kit was simply sanded off and returned to the protective case.

Figure 6. Camouflage waterproof backpack cover (photo from the website https://545design.ru )

In addition to camouflage coloring of uniforms and covers, other methods of camouflage are used: distortion of the contour of the figure due to capes, baggy cut of uniforms and patchwork suits, the use of local objects and materials – branches and dirt, etc.

In modern conditions, when technical means of reconnaissance and surveillance began to play an essential role on the battlefield, the range used by optics expanded: the ultraviolet part (Ultraviolet, UV) was not used due to the peculiarities of its absorption by the atmosphere, but in addition to the visible (visible L ight S spectrum, VS, Vis), it began to be actively used and the infrared part of the spectrum (Infrared, IR). Accordingly, suits and multi-layered fabrics are added to the camouflage in the visible range, providing reduced visibility in the infrared, and sometimes in the radar spectrum.

4. About the disguise of military equipment

Another important area of application of stealth methods is the masking of military equipment, which makes it difficult to detect and identify it. Unlike the masking of personnel, the principles of optical masking of equipment depend significantly on the time of day. In the dark, secrecy is ensured by blackout, both by using special blackout devices installed on headlights and parking lights, and by using night vision devices to control equipment without turning on lighting devices. In some cases, to reduce the level of visibility when working on machinery, lighting devices operating in the rapidly fading ultraviolet part of the spectrum, for example, a blue shade, can be used to illuminate workplaces. And for lighting systems inside military equipment, electromechanical devices can be used that automatically open lighting circuits when opening doors or hatches.

In the daytime, as for military uniforms, secrecy is ensured by protective monochrome or camouflage coloring, distortion of the contours of objects by visual methods or physical means.

Work on the creation of camouflage painting options for equipment began during the First World War. First of all, which is logical, the equipment used directly on the battlefield was camouflaged – tanks, armored vehicles, anti-tank artillery. After the end of hostilities, these works were stopped, military equipment, for the sake of saving money, began to be painted in a monochrome protective color. The exception, perhaps, was the French army, in which military equipment was painted in camouflage colors until the beginning of World War II (Figure 7).

However, in most armies of the world, camouflage, including equipment and structures, was not yet considered as a separate section of engineering support, and the lack of regulation of their implementation processes lowered the status of camouflage measures. An example is the "Technical Regulations TR 195-45" of 1926 and the "Instructions for performing engineering tasks in the field" of 1932 of the US Armed Forces, in which practically no attention was paid to the issues of camouflage ^[7].

With the outbreak of hostilities, some armies returned to applying camouflage coloring to tanks, for example, some tanks and self-propelled guns were crucified in the Wehrmacht. In the Soviet army, factory camouflage colors were applied only to reconnaissance armored vehicles.

Figure 7. A variant of the camouflage coloring of the Char-B1 heavy tank (photo from the website https://ru.wikipedia.org/wiki/Char_B1 )

Thus, both during the world Wars and later, when painting military equipment, specialized stained circuits were used to provide optical distortion of the contours of hidden objects. These schemes were formed exactly according to the same principles as for camouflage uniforms, differing in the type of pattern and the number of colors, which, in turn, were determined by the characteristics of the theater of operations (Figure 8).

Figure 8. Variants of camouflage coloring of the M113 armored personnel carrier of different armies (photo from the Internet)

That is, in general, the principles of creating camouflage coloring of equipment in the armies of different countries correspond to those used in camouflage uniforms and other means of disguising personnel. Including, for example, the principles of applying camouflage makeup, when lighter tones are used to paint convex surfaces and corners, and dark tones are used for hollows and niches.

Similar principles are implemented when using modern "digital" coloring schemes (Figure 9, 10).

Figure 9. Pixel tricolor coloring of a combat helicopter (photo by the author from the MAKS-2021 exhibition)

Figure 10. Pixel four-color coloring of the main battle tank KF51 (photo from the website naked-science.ru )

Sometimes, along with standard camouflage options and factory coloring, camouflage methods are used, implemented directly in the troops. A fairly common example is when winter camouflage is provided by applying a lime solution to the equipment, as was done during the Second World War. Or, for example, the shelter of equipment with felled branches ^[5]. To date, the method of staining objects with mud is used according to the schemes given in the technical documentation for various types of weapons ^[8].

In the conditions of modern conflicts, which are mainly fought in urban areas, various utilitarian objects can be used as improvised materials. For example, during the exercises of the Bundeswehr, the Marder infantry fighting vehicles were disguised using household garbage (Figure 11).

Figure 11. Masking the Marder BMP with improvised means

The use of local materials not only reduces the cost of the masking process, but also provides a natural coloring of one of the shades of the camouflage pattern to match the background of the area.

In addition to painting and using the protective properties of the terrain, other methods are used to ensure the secrecy of equipment: in the optical range – camouflage nets and screens of various types, aerosol curtains, hiding from observation in natural shelters and engineering structures, and in the acoustic – technical methods of noise reduction or hiding the operation of engines and moving equipment with third-party noise, etc.

Regarding the use of aerosol curtains, it can be recalled that even during the First World War, troops and equipment were covered by mobile smoke installations, smoke artillery ammunition appeared. During the Second World War, smoke grenade launchers began to be installed on individual armored vehicles, as on German Tiger tanks (Pz.Kpfw.VI Tiger), or individual smoke exhaust devices, like BDSH-5 on Soviet T-34-85. Now almost all military equipment is equipped with such means: both smoke grenade launchers for setting aerosol curtains in the course of movement, and a fuel injection device into the exhaust system to create a cloud of artificial fog.

Regular smoke grenade launchers continue to be improved, ensuring the creation of smoke masks of a more effective composition, providing both protection in different ranges of the spectrum, not only in the optical range, but also in infrared and radar, as well as stealth from different angles, for example, from above. There is information in open sources about attempts to develop means of setting smoke screens with unilateral permeability, ensuring the concealment of their troops from the enemy without interfering with the review.

Sets of camouflage nets and screens used to hide equipment and positions are also being actively improved: a more advanced and diverse coloring is being created, the range of their protection is expanding – in addition to optical, a number of camouflage nets provide dispersion or absorption of radar and infrared radiation. The requirements for camouflage kits for equipment are also changing, for example, due to the transition from the use of camouflage nets to sets of light screens of various shapes, providing the construction of surfaces of complex shapes and having the ability to be placed on both stationary and moving equipment. An example is the LCSS (Lightweight Camouflage Screen System) camouflage kit of the US Armed Forces, consisting of diamond-shaped and hexagonal masks made of modern synthetic materials, as well as their fastening means.

All these changes were reflected in the guidance documents on engineering support in terms of camouflage measures. For example, the US Armed Forces are FM 5-20 "Basic principles of concealment and their implementation in combat" in 1959 and 1968, the FM 20-3 "Concealment" field charter of 1990, technical regulations TB 43-0209 "Coloring of military equipment, property and equipment" and others.

A separate section of object masking can be considered to ensure the secrecy of naval equipment. As in the land forces, since the days of the sailing fleet, silhouettes, flag and other colors of ships have served to identify and simplify management in the campaign and in battle. Little has changed with the arrival of mechanical propulsion, rifled artillery and armor to the fleet. The importance of optical camouflage was appreciated by fleet specialists only at the beginning of the twentieth century. Prior to this period, most fleets painted ships black, and individual parts were generally painted in bright colors, for example, superstructures and pipes were painted brown or even yellow. The Russian-Japanese war forced a rethink of this approach, and by the beginning of the First World War, warships and auxiliary vessels of the world's leading fleets were colored in shades of gray. In the Russian Navy during this period, a method of uneven protective coloring of ships was developed — a darker color of the hull and lighter superstructures and pipes, which ensured the "blurring" of the silhouettes of ships against the sky.

In the maritime business, quite unusual, extravagant approaches to disguise were also used. During the First World War, such a type of camouflage appeared as "Dazzle camouflage", made in the form of a set of bright intertwining lines that make it difficult to determine the contours and direction of movement of the ship ^[9]. In aviation, a similar idea was implemented by applying an image of a cockpit lantern to the lower part of the aircraft, as the pilots of the Finnish Brewster F2A sometimes did during World War II, trying to confuse the pilots of enemy fighters regarding the direction of their maneuver. However, this approach, as well as the "blinding" camouflage, work more due to the effect of surprise, that is, for a fairly short time. Further, when the enemy understands the principle of deception, the approach ceases to create the desired effect, and originality, as in the case of "blinding" camouflage, begins to play against the user, giving out the location with an unusual color, but no longer deceiving the enemy.

Over time, the developers of ship camouflage schemes came to a compromise – ships began to be painted in colors of various shades of gray, but the pattern was applied so that the contours of the silhouette of the ship were distorted. Ship camouflage schemes in one variation or another continue to be used, but given that with increasing combat distance and the appearance of homing ammunition, it has become much more important to reduce the visibility of ships and vessels in the radar and thermal, rather than in the optical range. In modern conditions, optical camouflage remains relevant only for small ships operating against an enemy that has no other means of reconnaissance other than optical ones, for example, for patrol and anti–sabotage boats (Figure 12).

Figure 12. Camouflage coloring of the Raptor patrol boat (photo from the website www.mil.ru )

And, of course, the logical development of the process of ensuring secrecy in the fleet was the appearance of submarines hiding from observation under a layer of water. The boats themselves, given that they rose to the surface to charge the batteries, as a rule, at night, were painted black, and the main efforts to ensure secrecy were directed at increasing the time spent underwater, reducing noise and demagnetization.

With the advent of aviation over the battlefield, it was necessary to mask aircraft, mainly combat ones. According to the experience of combat operations, the following approach was formed – from detection on the ground, aircraft were hidden with khaki paint or camouflage coloring of the upper part of the fuselage and wings, and in the air, painting the bottom in gray-blue tones. The colors and shades of aviation camouflage varied depending on the country of manufacture of aircraft and theater of operations. For example, during the Second World War, the Luftwaffe used several types of fighter and bomber camouflage: different versions of a mixture of colors and shades, each of which had its own alphanumeric designation. The type of camouflage was indicated by listing the shades used, for example, the gray camouflage "RLM 74/75/76". In the Red Army during this period, two variants of aircraft coloring were installed: the basic "factory" dark green in the upper part and from the sides, gray (gray-blue) in the lower part, plus a variable crucifixion applied in the troops with casein paints. Variants of the camouflage pattern differed for fighter, bomber and assault aircraft. Although the color of the aircraft received by the USSR from the allies, as a rule, was not changed. For example, American aircraft arriving under lend-lease remained in the uniform gray-green color of Olive Drab 41 ^[5].

The schemes of aviation camouflage were improved based on the results of the analysis of the experience of combat use. One of these requirements was the use of matte paints that do not give glare during maneuvers of the aircraft. Aircraft for night use were sometimes painted black. In the second half of the twentieth century, with the development of radar and an increase in the distance of air combat, less attention was paid to optical camouflage and aircraft were simply left with the color of the hull material, polished duralumin or steel, without impairing the aerodynamics by painting. However, the decrease in visibility turned out to be necessary and, over time, combat aircraft began to paint the sky from below and camouflage the color of the terrain from above.

The essence of ensuring the stealth of flying objects was the stealth technology. However, the main efforts in it are focused on reducing the effective scattering surface in the radar range and reducing visibility in the infrared region, and in the optical spectrum, visibility was reduced by the long-proven use of black matte coatings for actions at night.

With the advent of unmanned aerial vehicles, slow and low-flying, the problem of the effectiveness of increasing stealth in the optical range for objects operating in the air has returned to relevance.

5. Increasing the secrecy of stationary structures and rear facilities

Describing the methods of reducing the optical visibility of objects, it is impossible not to mention the methods of protecting rear objects, masking buildings and special structures. For a fairly long historical period, this problem was not very relevant. In 1935, the doctrine of "total war" (German: Durchf?hrung des totalen Krieg), proposed by German General E. Ludendorff (Erich Friedrich Wilhelm Ludendorff), was published, according to which not only military formations and the nearest rear, but also the infrastructure of the enemy state, including civil, were subject to defeat. As a result of its practical implementation in a number of subsequent wars and conflicts, there was a need to protect large facilities, sometimes entire cities. In addition to covering them with air defense forces, as it turned out, camouflage can also be used. An example of the latter is the complex camouflage of Moscow, Leningrad and Sevastopol during the Great Patriotic War. This disguise, taking into account the characteristics of the means of reconnaissance and destruction of that time, was carried out in two directions: day and night.

In terms of daytime camouflage measures, for example, in Leningrad, which became a frontline city, the contours of the most prominent buildings were distorted: the golden domes of cathedrals were repainted in gray, the spire of the Peter and Paul Church was covered with a tarpaulin. And in Moscow, a group of architects and engineers led by Academician Boris Iofan developed a whole range of measures to ensure secrecy: planar (by false coloring) and volumetric (by building false structures, including on water) masking the center of the capital (Figure 13) A grandiose project, coupled with other protection measures, fulfilled its function. If the enemy's air reconnaissance could, with a detailed analysis, reveal false targets and determine the position of the real ones, then the German pilots participating in the raids, in conditions of limited time to assess the situation, could not perform targeted bombing at specified targets.

The creation of false objects showed high efficiency, especially those simulating the residual illumination of industrial enterprises at night. In total, seven mock-ups of factory buildings, two mock-ups of grain elevators, an oil depot and nine false airfields with high detail were built around Moscow. According to the objects, the enemy used, according to various estimates, from six to nine percent of all bombs used in the raids.

Figure 13. The masking of the Bolshoi Theatre in 1941. Photo by Margaret Burke-White (photo from the website https://kerchtt.ru )

However, all of these methods are largely improvisational, generated by forced measures when approaching the front line. More interesting from the point of view of the study is the option of advance masking. So, some historians believe that the projects of a number of Stalin's dachas, designed by architect Merzhanov, are an example of just such preparation. They provide optical concealment of buildings by using an uneven surface coating of the "fur coat" type and painting with the color "chromepik". Of course, this is only a version, but judging by the appearance of the buildings, it has the right to exist (Figure 14).

Figure 14. Painting of Stalin's dacha in the New Matsesta (photo by the author)

But disguising protected defense facilities as general–purpose buildings is a typical method of mimicry, also borrowed from nature. For example, during the Second World War, elements of the central command post of the Supreme Command of the Wehrmacht Land Forces (Oberkommando des Heeres) in W?nsdorf, along with sinking into the ground, masqueraded as ordinary residential buildings. However, making exits from bunkers in the form of general–purpose buildings is a well-known practice.

These methods of disguise were used during daylight hours. The main method of ensuring the secrecy of rear objects at night was blackout. For its implementation, a whole range of organizational measures, both planning and control, was carried out.

It should be noted that the stationary objects to be masked were not only in the rear, but also in advanced positions and in the frontline. In their disguise, approaches based on deepening and mimicry for local objects were mainly used. The most striking example in this regard can be considered the defensive structures of the well-known "Mannerheim line" (fin. Mannerheim-linja), which perfectly fit into the Karelian landscape.

However, as in many other areas, the most effective way to ensure secrecy is the integrated application of existing methods. A vivid historical example is the fighting of the 411th coastal battery in the defense of Odessa in August-October 1941. Comprehensive protection measures were implemented on a battery of 180 mm guns built in the 30s: guns located in concrete artillery lodgments (Figure 15) were covered with removable shields imitating local objects, command posts and supply facilities were hidden underground, and a false firing position was formed half a kilometer from the battery. As a result, despite the intensity of the fighting, during which the battery completed over 220 fire missions, repelled several enemy air raids, the battery had no losses of guns and personnel.

Figure 15. Positions of the 411 coastal battery gun (photo by the author)

6. Other measures to ensure secrecy

These methods relate to measures to reduce the visibility of objects in the optical range, mainly in its visible part. Of course, in various conditions of warfare, it is necessary to fend off other unmasking factors. For example, when conducting fleet operations, acoustic methods of detecting the enemy are often used. Accordingly, ships and submarines use acoustic masking methods, both passive and active. With the spread of radar reconnaissance and guidance, it was necessary to develop measures to ensure secrecy in the field of radio waves. To do this, back in the middle of the last century, the equipment began to be equipped with means of passive masking and jamming, and subsequently with active suppression of enemy radar. In the USSR and leading foreign countries, camouflage networks and screens were developed to ensure the absorption or scattering of radar and infrared radiation ^[5].

To ensure stealth in various ranges, including in the infrared part of the spectrum, which began to be actively used with the development of technical means of reconnaissance and aiming, other technical means are also used: absorbing and reflecting screens, radar corner reflectors, devices for reducing exhaust gas temperature by mixing cold air with them, etc. The range of tools and methods is quite wide and has not yet been fully used.

Personal protective equipment also began to provide protection not only in the visible spectrum of the optical range. An example is multilayer camouflage thermal and radio scattering suits designed to protect military personnel from optoelectronic, thermal and radar reconnaissance equipment.

Another approach to protecting objects is to divert attention from important targets and switch enemy intelligence efforts to false objects. Experts define this approach as imitation and demonstration actions ^{[10, 11, 12]}.

With the advent of thermal imaging devices and ammunition with guidance systems in the infrared spectrum, units began to equip IR traps to create a local artificial thermal field in which less contrasting real targets can be lost for homing vehicles. In the radar spectrum, different types of reflectors are used for this purpose.

7. About some other camouflage applications

As historical analysis shows, camouflage is used not only for its intended purpose, in military affairs, but also for other purposes, sometimes far from the field of armed confrontation.

One of the notable aspects is the use of camouflage fabrics in fashion. Practice has shown that after every major war, there are unspent stocks of weapons, equipment and uniforms. It does not always make sense to keep them, the peacetime army does not need them. Therefore, stocks are most often sold at discounted prices. An example is the history of the Leroy Merlin chain, which began with the Au Stock Americain stores selling property and equipment left by the American army in the northern towns of France after the First World War, because it was simply not profitable to export them from Europe.

The practical and durable army uniform, including camouflage, was liked by many even after the Second World War. And in the 60s of the last century, after the end of a series of national liberation and anti-colonial wars, the widespread use of military uniforms gave rise to the military style. Camouflage clothing elements were notable components of this style. In the 70s of the last century, the "military" style became a symbol of various youth subcultures, protests against wars and violence. And to this day, elements of the "military" style remain relevant: rough boots, elements of army equipment used as brutal accessories and, of course, camouflage jackets, trousers, caps and scarves.

Now, again, as in the 70s, camouflage as durable and non-marking clothing is becoming a symbol of street protests. A baggy silhouette and a cap with a visor play a certain role in this, making it difficult to visually identify the protesters by means of video recording and identification. With this in mind, in some countries, wearing camouflage clothing at mass events is not recommended ^[5].

Another notable trend in the use of camouflage in the civilian sphere is the use of camouflage suits and capes by hunters and tourists. It should be noted that there are certain differences in this area of camouflage, determined by the peculiarity of animals that most of them have dichromatic vision, which does not allow them to distinguish many colors. Therefore, specialized hunting camouflage sometimes simultaneously solves two tasks: it provides a crucifixion of the hunter's silhouette to make it less noticeable to animals, and marks the hunter to show his position to his companions. Based on this, it often comes in bright shades: red, pink.

However, all these aspects are rather side effects, the main purpose of camouflage was and remains to be used in the military field.

8. Some conclusions

Thus, the historical analysis allows us to carry out the following classification of methods for reducing optical visibility, clarifying the existing one:

1) by the type of masked object:

- personnel;

- equipment and weapons on the battlefield;

- equipment of the nearest rear area;

- objects of the rear.

2) according to the methods and materials used:

- factory protective, including camouflage paint;

- standard means of hiding and distorting the contours of objects (masking networks and screens);

- means of dynamic shielding (fumes and aerosols);

- improvised means and materials;

- concealment using engineering structures, local objects or terrain features;

- the method of mimicry for local objects, non-military structures or less important objects;

3) according to the operating environment of the protected objects:

- ground facilities;

- marine facilities;

- aerial objects in the air and on the ground;

4) in relation to the time of day (light or dark), by season or by region of action.

This list is formed relative to the "classical" approach to masking objects, hiding their location on the ground. In the context of modern conflicts, characterized by the high intensity of the use of unmanned reconnaissance vehicles, the use of high-precision weapons and structurally selective approaches to hitting objects, there is a need to implement other approaches to ensuring protection. Not being able to reliably hide an object in conditions of high density of reconnaissance UAVs, you can take advantage of the fact that the enemy's resource is not infinite, the cost of high-precision ammunition is high, and distract his attention using false objects or mimicry of protected objects for less important ones, taken to defeat in the last place. Examples of such mimicry caused by combat necessity have already been in history during the Second World War.

So, in 1944, the M4 Sherman tank, whose fire capabilities to combat new German tanks reached the limit, was upgraded by installing a QF-17 long-barreled cannon (Quick Firing 17-pounder). The new, more effective modification of the Sherman Firefly externally began to differ greatly from the basic version of the M4 in barrel length, but was often used in conjunction with it. In order to prevent increased losses of modernized tanks from enemy fire, for which they were priority targets, an unusual "wavy" camouflage color of the barrel of the tank's cannon was used. It was performed from its middle to the muzzle to visually hide the increased length of the gun and make it difficult to recognize the upgraded version among the regular M4.

An equally vivid example is the modification of the T–34 tower of Nizhny Tagil Plant No. 183 in 1943-44: after installing a second observation device for the commander on a new tower, so that the commander's tank with two "mushrooms" did not stand out among the linear ones, a mock-up of the second periscope was welded on the towers of all other tanks, which does not have functionality, but looks like a real one. True, combat experience, like any other, is forgotten over time, and already in the 80s of the last century, during the Afghan War, the commander's armored personnel carriers of the Soviet army were so outwardly different from the linear ones that it was visually possible to determine this at almost all ranges of use of weapons.

Another application of the mimicry method is to get lost among similar ones, in the case of masking objects and equipment, this is achieved by creating false objects. During the Second World War, special imitation units were used for this purpose, creating false samples of equipment and entire objects from improvised means, for example, airfields. Currently, mock-ups of equipment are being manufactured industrially, which have not only the visual characteristics of real samples, but also a similar thermal portrait. Similar measures were used in other ranges of camouflage: during the Second World War, to hide the places of artillery firing positions from sound reconnaissance, the method of detonating charges simulating firing was used, away from the actual location of the guns.

Using the method of analogies, it can be assumed that a similar classification can be used with respect to masking when protecting against surveillance in other areas of the optical range and the radio-electronic spectrum: infrared, radar. The transition to military operations in a multi-domain space (MDB) requires secrecy not only in the physical, but also in the information field. This factor requires the organization of protection against other means of intelligence, such as cyber intelligence, radio and radio engineering intelligence, which should be provided by a slightly different set of measures, which was not considered in this article.

At the same time, the analysis of the state of the subject area allows us to conclude that, despite the change in the conditions of warfare, "ordinary" army camouflage has not lost its importance in modern conditions. And, probably, it will not lose in the future.

Moreover, at present, the development of camouflage has become so effective that it required solving the inverse problem – to return the identification functions to the military uniform, at least partially. Recently, often in video reports from areas of local wars and armed conflicts, you can see how the opposing sides add colored components to the uniform – armbands or headbands. This is done precisely in order to distinguish between our own and others dressed in camouflage in the conditions of dynamic combat operations. A similar approach is implemented for recognizing equipment, for example, applying colored stripes or signs that are easily distinguishable from the ground and air, especially when the parties to the conflict use the same type of equipment and identification by silhouettes is impossible. Other, more technologically advanced methods of recognition on the battlefield are also used. For example, for NATO aviation, the IFF (Identification Friend or Foe) standard aviation system is used, a CID (Cooperative Identification and Designation) system is implemented at ground facilities, including BTID-type devices installed on equipment, as well as means of identifying millimeter-range targets with the Cooperative Target ID System and optoelectronic DSID (Dismounted Soldier Identification Device) used by personnel ^{[1, 13]}.  However, the development of technology is cyclical, now there is a need to hide the sources of signals of these systems from the enemy

Conclusion

Thus, it can be concluded that masking in the optical spectrum, in all its ranges, remains quite relevant in modern conditions.

Firstly, despite the appearance on the battlefield of surveillance and aiming devices operating not only in the visible, but also in the infrared and radio bands, optical camouflage is still very important to reduce losses of personnel and equipment. And the use of historical experience, proven methods of reducing optical visibility, remains relevant.

Secondly, it would be logical to expect the spread of the principles of using camouflage colors to implement such properties in all angles and ranges, including taking into account the peculiarities of the technical vision of unmanned vehicles, which are becoming more and more on and above the battlefield ^{[14, 15, 16]}. This thesis seems to be especially relevant for autonomous UAVs. The principles developed for optical masking and tested in practice can be used to solve similar problems in other ranges and environments. And, given the multidomain nature of modern warfare, not only in the physical sphere.

Thirdly, the potential for the development of camouflage means has not yet been exhausted: on the one hand, the development of autonomous robotics and the active appearance of robotic systems on the battlefield requires increased stealth from technical vision, on the other – and the process of borrowing from nature, from which, in fact, the development of camouflage began, has not yet been fully realized. There are, for example, living beings that dynamically change color according to the situation, and this natural property was tried to be repeated by experts from Seoul National University, who developed artificial skin that changes color when the temperature of nanowire heating elements controlled by a computer changes. The created coating can not only change color, but also form patterns. Similar work is being carried out quite successfully in Japan. The materials being developed are still expensive and incomplete prototypes, but with prospects for use in optical masking practice as technology develops. It is quite possible that the same approach can be used in other ranges, for example, in infrared, by bringing the IR radiation of an object to the background level by equipping it with temperature sensors and distributed means of individual air conditioning. Moreover, analogues of this approach can be found in history – during the war, snipers, being in ambush, deliberately chewed snow to cool their breath and not give themselves away with steam from their mouths. According to a similar principle, exhaust gases were cooled on some samples of military equipment by mixing atmospheric air.

In addition to the above examples, there are a number of other natural properties and methods of camouflage, for example, mimicry of color, shape, sounds or even smells for other animals or plants, for local objects, and other protection options. Despite the growth of technological capabilities, much of what is available in nature has not yet been realized in disguise. Work in this area is likely to continue in the future ^[17-20].

Fourth, the search for new methods of disguise can be carried out not only by borrowing from nature or using new technologies. There may be other options, for example, the use of the so-called "Columbus principle", described back in the Soviet theory of inventive problem solving (TRIZ). The method consists in identifying and using useful side properties of an object or phenomenon that arise in addition to its main function. A historical example of this option is the use of the zimmerite material (German Zimmeri t) to protect the German Tiger and Panther tanks from magnetic mines. The resulting armor coating, formed from a binding agent and fillers, not only reduced the possibility of fixing mines on the armor, but also, due to the application features, provided a rough and glare-free camouflage coating of the protected equipment. Which increased secrecy, although such a goal was not originally set. The opposite phenomenon has already been mentioned – the appearance of additional properties in disguises, such as, for example, water resistance in camouflage gear covers. The identification and use of such side beneficial properties in the interests of solving important tasks, if necessary, with some modifications, is one of the promising directions for the development of any technology, not excluding the technology of increasing secrecy.

Fifthly, analyzing the still unrealized potential opportunities for increasing stealth, it is worth considering that the main purpose of disguise is to make sure that the enemy does not see what actually exists, could not correctly assess the objects and the situation. Understanding this, it can be concluded that ensuring secrecy can be realized not only through the use of optical illusions to deceive vision, but also through directed distortion of the observer's understanding of information, that is, deception of the human brain or algorithms of machine vision systems. The point is that the development of information technologies, the use in management practice of technical means of collecting and processing information, augmented reality (AR) and virtual reality (VR) technologies, generates new opportunities in purposefully distorting information about objects given to the observer. There is already an example of constructing a camouflage pattern based on the analysis of vulnerabilities of neural network recognition algorithms, due to the implementation of which an object normally distinguishable by a person is not recognized by hardware and software surveillance complexes. In the future, such, and even broader possibilities, can be realized by distorting or adding virtual information about real objects that change their perception, which, in theory, may even give rise to new directions in disguise.

And the last thing: As historical analysis shows, methods of increasing stealth are effective not only when they are rationally prepared, but also when they are used in combination and purposefully, combined with other measures to mislead the enemy, implemented both directly on the battlefield, at the tactical level, and in higher instances. Including, as already noted, in a wide variety of ranges and spheres. And, as historical experience shows, all camouflage measures should be carried out taking into account the likely time of their opening by enemy intelligence, that is, they should be clarified and updated in a timely manner.

These factors, both of a historical nature and implemented in modern times, must be taken into account both when developing camouflage systems and organizing the practical application of camouflage technologies.