Editing Smoke screen

{{Short description|Airborne obscurant using gas and particulates}}
{{Other uses|Smokescreen (disambiguation)}}
{{More citations needed|date=August 2009}}
[[File:Massachusetts National Guard (27773978964).jpg|thumb|upright=1.35|Soldiers advancing under the cover of a smoke screen during a [[Military exercise|training exercise]]]]

A '''smoke screen''' is [[smoke]] released to mask the movement or location of military units such as [[infantry]], [[tank]]s, [[aircraft]], or [[ship]]s.

Smoke screens are commonly deployed either by a [[wikt:canister|canister]] (such as a [[Smoke grenade|grenade]]) or generated by a vehicle (such as a [[tank]] or a [[warship]]).

Whereas smoke screens were originally used to hide movement from enemies' line of sight, modern [[technology]] means that they are now also available in new forms; they can screen in the [[infrared]] as well as [[visible spectrum]] of light to prevent detection by infrared sensors or viewers, and they are also available for vehicles in a super-dense form used to block laser beams of enemy [[laser designator]]s or [[rangefinder]]s.

==Technology==
===Smoke grenades===
{{Main|Smoke grenade}}
[[File:171029-M-MN519-0191 (37534718814).jpg|thumb|A [[French Foreign Legion|French Legionnaire]] moving through a smoke screen generated using a smoke grenade]]
These are canister-type [[grenades]] used as a ground-to-ground or ground-to-air signalling device. The body consists of a steel sheet metal cylinder with a few emission holes on the top and/or bottom to allow smoke release when the [[smoke composition]] inside the grenade is ignited. In those that produce [[colored smoke]], the filler consists of 250 to 350&nbsp;grams of colored (red, green, yellow or violet) smoke mixture (mostly [[potassium chlorate]], [[sodium bicarbonate]], [[lactose]] and a [[dye]]). In those that produce screening smoke, the filler usually consists of HC smoke mixture (hexachloroethane/zinc) or TA smoke mixture (terephthalic acid). Another type of smoke grenade is filled with [[white phosphorus incendiary|white phosphorus]] (WP), which is spread by explosive action. The phosphorus catches fire in the presence of air, and burns with a brilliant yellow flame, while producing copious amounts of white smoke (phosphorus pentoxide). WP grenades double as [[incendiary grenade]]s.

===Smoke shell===
{{See also|Shell (projectile)#Smoke}}
[[Artillery]] and [[mortar (weapon)|mortar]]s can also fire smoke generating munitions, and are the main means of generating tactical smokescreens on land. As with grenades, artillery shells are available as both emission type smoke shell, and bursting smoke shell. Mortars nearly always use bursting smoke rounds because of the smaller size of mortar bombs and the greater efficiency of bursting rounds.

===Smoke generators===
[[File:Challenger 2 Tank MOD 45154622.jpg|thumb|A [[British Army]] [[Challenger 2]] deploying a smoke screen using a smoke generator installed in its rear]]
[[File:JGSDF Smoke generator equipment(High Mobility Vehicle,Right Rear View) at Camp Shinodayama April 24, 2016.JPG|thumb|A [[Japan Ground Self-Defense Force|JGSDF]] [[Toyota Mega Cruiser]] with a smoke generator installed in its rear compartment]]
Very large or sustained smoke screens are produced by a smoke generator. This machine heats a volatile material (typically oil or an oil based mixture) to evaporate it, then mixes the vapor with cool external air at a controlled rate so it condenses to a mist with a controlled droplet size. Cruder designs simply boiled waste oil over a heater, while more sophisticated ones sprayed a specially formulated oily composition ("fog oil") through nozzles onto a heated plate. Choice of a suitable oil, and careful control of cooling rate, can produce droplet sizes close to the ideal size for [[Mie theory|Mie scattering]] of [[visible light]]. This produces a very effective obscuration per weight of material used. This screen can then be sustained as long as the generator is supplied with oil, and&mdash;especially if a number of generators are used&mdash;the screen can build up to a considerable size. One 50 gallon drum of fog oil can obscure {{convert|60|mi|km}} of land in 15 minutes.

Whilst producing very large amounts of smoke relatively cheaply, these generators have a number of disadvantages. They are much slower to respond than pyrotechnic sources, and require a valuable piece of equipment to be sited at the point of emission of the smoke. They are also relatively heavy and not readily portable, which is a significant problem if the wind shifts. To overcome this latter problem, they may be used in fixed posts widely dispersed over the battlefield, or else mounted on specially adapted vehicles. An example of the latter is the [[M56 Coyote]] generator.

Many [[armoured fighting vehicle]]s can create smoke screens in a similar way, generally by injecting [[diesel fuel]] onto the hot [[exhaust system|exhaust]].

===Naval methods===
[[File:US Navy 090425-N-4879G-393 A group of multinational amphibious assault vehicles from the amphibious dock landing ship USS Ashland (LSD 48) deploy smoke to cover their landing during a simulated amphibious landing demonstration.jpg|thumb|[[Assault Amphibious Vehicle]]s deploying smoke to cover their landing]]
Warships have sometimes used a simple variation of the smoke generator, by injecting fuel oil directly into the funnel, where it evaporates into a white cloud. An even simpler method that was used in the days of steam-propelled warships was to restrict the supply of air to the boiler. This resulted in incomplete combustion of the coal or oil, which produced a thick black smoke. Because the smoke was black, it absorbed heat from the sun and tended to rise above the water. Therefore, navies turned to various chemicals, such as [[titanium tetrachloride]], that produce a white, low-lying cloud.<ref>{{cite video
 | title = The Royal Navy at War
 | medium =DVD
 | publisher =[[Imperial War Museum]]
 | location =London
 | date =2005}}</ref><ref>{{Cite web
  | title = Smoke
  | work = Treatment of Chemical Agent Casualties and Conventional Military Chemical Injuries
  | publisher = Department of Defense, Washington DC
  | date = 22 December 1995
  | url = http://www.globalsecurity.org/wmd/library/policy/army/fm/8-285/ch8.pdf
  | access-date = 27 May 2011}}</ref>

==Infrared smokes==
The proliferation of [[Thermography|thermal imaging]] [[Forward-looking infrared|FLIR]] systems on the battlefields necessitates the use of obscurant smokes that are effectively opaque in the [[infrared]] part of electromagnetic spectrum. This kind of obscurant smoke is sometimes referred to as "Visual and Infrared Screening Smoke" (VIRSS).<ref>{{cite book|page=119|url=https://books.google.com/books?id=62VtBQAAQBAJ&q=%22Visual+and+Infrared+Screening+Smoke%22&pg=PA119|title=The Armed Forces of the United Kingdom 2014-2015|first=Charles|last=Hayman|date=10 February 2014|access-date=14 April 2018|publisher=Pen and Sword| isbn=9781783463510 |via=Google Books}}</ref> To achieve this, the particle size and composition of the smokes has to be adjusted. One of the approaches is using an aerosol of burning [[red phosphorus]] particles and [[aluminium]]-coated glass fibers; the infrared emissions of such smoke curtains hides the weaker emissions of colder objects behind it, but the effect is only short-lived. [[soot|Carbon]] (most often [[graphite]]) particles present in the smokes can also serve to absorb the beams of [[laser designator]]s. Yet another possibility is a water [[fog]] sprayed around the vehicle; the presence of large droplets absorbs in infrared band and additionally serves as a countermeasure against [[radar]]s in [[W band|94 GHz]] band. Other materials used as visible/infrared obscurants are micro-pulverized flakes of [[brass]] or [[graphite]], particles of [[titanium dioxide]], or [[terephthalic acid]].

Older systems for production of infrared smoke work as generators of [[aerosol]] of [[dust]] with controlled particle size. Most contemporary vehicle-mounted systems use this approach. However, the aerosol stays airborne only for a short time.

The [[brass]] particles used in some infrared [[smoke grenade]]s are typically composed of 70% [[copper]] and 30% [[zinc]]. They are shaped as irregular flakes with a diameter of about 1.7&nbsp;μm and thickness of 80–320&nbsp;nm.<ref>[http://orsted.nap.edu/openbook.php?record_id=9621&page=45 orsted.nap.edu] {{webarchive|url=https://web.archive.org/web/20070225010747/http://orsted.nap.edu/openbook.php?record_id=9621&page=45 |date=2007-02-25 }}</ref>

Some experimental obscurants work in both infrared and [[millimeter wave]] region. They include [[carbon fiber]]s, metal coated fibers or [[glass]] particles, metal microwires, particles of iron and of suitable polymers.<ref>{{cite web|url=http://www.sew-lexicon.com/gloss_o.htm|title=sew-lexicon.com|url-status=dead|archive-url=https://web.archive.org/web/20000107061927/http://www.sew-lexicon.com/gloss_o.htm|archive-date=2000-01-07}}</ref>

==Chemicals used==
<!-- Abbreviated from FM 8-9 part III. Should be somewhat mixed with the content above. -->[[File:US Navy 100915-N-4894D-110 Marines participate in the 60th anniversary of teh Incheon Landing Operation.jpg|thumb|upright=1.2|Amphibious vehicles deploying smoke grenades]]

===Zinc chloride===
Zinc chloride smoke is grey-white and consists of tiny particles of [[zinc chloride]]. The most common mixture for generating these is a [[smoke composition|zinc chloride smoke mixture]] (HC), consisting of [[hexachloroethane]], grained [[aluminium]] and [[zinc oxide]]. The smoke consists of zinc chloride, zinc oxychlorides, and [[hydrochloric acid]], which absorb the [[humidity|moisture]] in the air. The smoke also contains traces of organic chlorinated compounds, [[phosgene]], [[carbon monoxide]], and [[chlorine]].

Its toxicity is caused mainly by the content of strongly acidic hydrochloric acid, but also due to thermal effects of reaction of zinc chloride with water. These effects cause [[lesion]]s of the [[mucous membrane]]s of the upper airways. Damage of the lower airways can manifest itself later as well, due to fine particles of zinc chloride and traces of phosgene. In high concentrations the smoke can be very dangerous when inhaled. Symptoms include [[dyspnea]], retrosternal pain, [[hoarseness]], [[stridor]], [[lachrymation]], [[cough]], [[expectoration]], and in some cases [[haemoptysis]]. Delayed [[pulmonary edema]], [[cyanosis]] or [[bronchopneumonia]] may develop. The smoke and the spent canisters contain suspected [[carcinogen]]s.

The prognosis for the casualties depends on the degree of the pulmonary damage. All exposed individuals should be kept under observation for 8 hours. Most affected individuals recover within several days, with some symptoms persisting for up to 1–2 weeks. Severe cases can suffer of reduced pulmonary function for some months, the worst cases developing marked dyspnoea and cyanosis leading to death.

Respirators are required for people coming into contact with the zinc chloride smoke.

===Chlorosulfuric acid===
[[Chlorosulfuric acid]] (CSA) is a heavy, strongly acidic liquid. When dispensed in air, it readily absorbs moisture and forms dense white fog of [[hydrochloric acid]] and [[sulfuric acid]]. In moderate concentrations it is highly irritating to eyes, nose, and skin.

When chlorosulfuric acid comes in contact with water, a strong [[exothermic]] reaction scatters the corrosive mixture in all directions. CSA is highly corrosive, so careful handling is required.

Low concentrations cause prickling sensations on the skin, but high concentrations or prolonged exposure to field concentrations can cause severe irritation of the eyes, skin, and respiratory tract, and mild cough and moderate [[contact dermatitis]] can result. Liquid CSA causes [[acid burn]]s of skin and exposure of eyes can lead to severe eye damage.

Affected body parts should be washed with water and then with [[sodium bicarbonate]] solution. The burns are then treated like thermal burns. The skin burns heal readily, while cornea burns can result in residual scarring.

Respirators are required for any concentrations sufficient to cause any coughing, irritation of the eyes or prickling of the skin.

===Titanium tetrachloride===
[[Titanium tetrachloride]] (FM) is a colorless, non-flammable, corrosive liquid. In contact with damp air it hydrolyzes readily, resulting in a dense white smoke consisting of droplets of hydrochloric acid and particles of titanium oxychloride.

The titanium tetrachloride smoke is an irritant and unpleasant to breathe.

It is dispensed from aircraft to create vertical smoke curtains, and during World War II it was a favorite smoke generation agent on warships.

Goggles and a respirator should be worn when in contact with the smoke, full protective clothing should be worn when handling liquid FM. In direct contact with skin or eyes, liquid FM causes acid burns.

===Phosphorus===
{{Main|White phosphorus (weapon)}}
Red [[phosphorus]] and [[white phosphorus incendiary|white phosphorus]] (WP) are red or waxy yellow or white substances. White phosphorus is [[Pyrophoricity|pyrophoric]] - can be handled safely when under water, but in contact with air it spontaneously ignites. It is used as an [[Incendiary device|incendiary]]. Both types of phosphorus are used for smoke generation, mostly in artillery shells, bombs, and grenades. <!-- effects of exposure? -->

White phosphorus smoke is typically very hot and may cause burns on contact. Red phosphorus is less reactive, does not ignite spontaneously, and its smoke does not cause thermal burns - for this reason it is safer to handle, but cannot be used so easily as an incendiary.

Aerosol of burning phosphorus particles is an effective obscurant against [[thermal imaging]] systems. However, this effect is short-lived. After the phosphorus particles fully burn, the smoke reverts from emission to absorption. While very effective in the visible spectrum, cool phosphorus smoke has only low absorption and scattering in infrared wavelengths. Additives in the smoke that involve this part of the spectrum may be visible to thermal imagers or IR viewers.<ref name="yarchive.net">{{cite web|url=http://yarchive.net/mil/infrared_smoke.html|title=Infrared smoke (Arno Hahma)|website=yarchive.net}}</ref>

===Dyes===
{{Main|Colored smoke}}
[[File:Smoke Signal 1.jpeg|thumb|Yellow smoke screens deployed to mark soldiers completing an objective during [[Exercise Northern Edge]] 2017]]
Various signalling purposes require the use of [[colored smoke]]. The smoke created is a fine mist of dye particles, generated by burning a mixture of one or more dyes with a low-temperature [[pyrotechnic composition]], usually based on [[potassium chlorate]] and [[lactose]] (also known as milk sugar).

Colored smoke screen is also possible by adding a colored dye into the fog oil mixture. Typical white smoke screen uses titanium dioxide (or other white pigment), but other colors are possible by replacing titanium dioxide with another pigment. When the hot fog oil condenses on contact with air, the pigment particles are suspended along with the oil vapor. Early smoke screen experiments attempted the use of colored pigment, but found that titanium dioxide was the most light scattering particle known and therefore best for use in obscuring troops and naval vessels. Colored smoke became primarily used for signaling rather than obscuring. In today's {{When|date=December 2019}} military, smoke grenades are found to be non-cancer causing, unlike the 1950s AN-M8 model.

===Sulfonic acid===
The smoke generator on the [[Medium Mark B]] tank used [[sulfonic acid]].<ref name=foss30>{{Cite book|title=The Vickers Tanks From landships to Challenger |last=Foss |first=Christopher F |author2=McKenzie, Peter  |year=1988 |publisher=Patrick Stephens Limited |isbn=1-85260-141-8 |page=30 }}</ref>

==Tactics==
===History===
[[File:Troops coming ashore from a landing craft under a smoke screen during Combined Operations training at Inveraray, Scotland, 9 October 1941. H14597.jpg|thumb|British and Scottish soldiers disembarking from a [[landing craft]] under a smoke screen, 1941]]

The first documented use of a smoke screen was circa 2000 B.C. in the wars of ancient India, where incendiary devices and toxic fumes caused people to fall asleep.<ref>A History of Chemical warfare by Kim Coleman (2005) (978-1-4039-3459-8)</ref>

It was later recorded by a Greek historian, [[Thucydides]], who described that the smoke created by the burning of sulphur, wood and pitch was carried by the wind into Plataea (428 B.C.) and later at Delium (423 B.C.) and that at Delium, defenders were driven from the city walls.<ref>{{Cite journal |last=ffoulkes |first=Charles |date=1940 |title=Fire, Smoke and Gas |url=https://www.jstor.org/stable/44219889 |journal=Journal of the Society for Army Historical Research |volume=19 |issue=75 |pages=144–148 |jstor=44219889 |issn=0037-9700}}</ref>

In 1622, a smoke screen was used at the [[Battle of Macau]] by the Dutch. A barrel of damp gunpowder was fired into the wind so that the Dutch could land under the cover of smoke.<ref>{{cite web | url=https://www.ohio.edu/news/2020/09/ohio-researchers-working-obscurants-modern-era#:~:text=One%20of%20the%20first%20recorded,landing%20under%20cover%20of%20smoke. | title=OHIO researchers working on obscurants for the modern era | date=28 September 2020 }}</ref>

Later, between 1790 and 1810, [[Thomas Cochrane, 10th Earl of Dundonald]] (1775–1860), a Scottish Naval commander and officer in the [[Royal Navy]] who fought during the French Revolutionary and Napoleonic Wars, devised a smoke screen created through the burning of sulphur which would be used in warfare after learning about the same methods used at Delium and Plataea.<ref>Lord Cochrane, Naval Commander, Radical, Inventor (1775-1860), A Study of His Earlier Career, 1775-1818 by John Sugden, July 1981. - https://etheses.whiterose.ac.uk/3466/1/290354.pdf</ref><ref>The Kalgoorlie Miner, Thu 11 Sep 1930 (Page 6)</ref>

[[Thomas Cochrane, 10th Earl of Dundonald]]'s grandson, [[Douglas Cochrane, 12th Earl of Dundonald]], described in his autobiography how he spoke to [[Winston Churchill]] (who once galloped for him when he had a brigade at manœuvres in England) of the importance of using smoke-screens on the battleground, it would in turn be used in both [[WWI]] & [[WW2]].<ref>{{Cite book |last= |first= |url=https://books.google.com/books?id=khHGxwEACAAJ |title=My Army Life |date=1926 |publisher=Edward Arnold & Company |language=en}}</ref>

===Land warfare===
[[File:Awm 128387 nadzab.jpg|thumb|right|A smoke screen obstructing the view of the parachute [[landing at Nadzab]], 1943]]
Smoke screens are usually used by infantry to conceal their movement in areas of enemy fire. They can also be used by [[armoured fighting vehicle]]s, such as [[tank]]s, to conceal a withdrawal. They have regularly been used since [[Early thermal weapons|earliest times]] to disorient or drive off attackers.

During the First World War the Germans used a lot of smoke screens (''Nebel'') to hide [[Batterie Pommern]].<ref>{{cite web|url=https://www.flickr.com/photos/feldpost14/albums/72157656806020692/with/15690769743|website=www.flickr.com |title=Batterij Pommern (Lange Max) - Koekelare - Moere |date=18 January 2015 }}</ref><ref>{{cite web|url=https://www.flickr.com/photos/feldpost14/26825063811/in/album-72157656806020692/|website=www.flickr.com |title=Rookpotten in de omgeving van batterij 'Pommern' (Lange Max) - Koekelare - Moere |date=8 May 2016 }}</ref><ref>{{cite web|url=https://www.flickr.com/photos/feldpost14/24638543822/in/album-72157656806020692/|website=www.flickr.com |title=Rookpotten in de omgeving van batterij 'Pommern' (Lange Max) - Koekelare - Moere |date=31 January 2016 }}</ref>

A toxic variant of the smokescreen was used and devised by [[Frank Arthur Brock]] who used it during the [[Zeebrugge Raid]] on 23 April 1918, the British Royal Navy's attempt to neutralize the key Belgian port of Bruges-[[Zeebrugge]].

For the crossing of the [[Dnieper river]] in October 1943, the [[Red Army]] laid a smoke screen {{convert|30|km|mi}} long. At the [[Operation Shingle|Anzio beachhead]] in 1944, US [[Chemical Corps]] troops maintained a {{convert|25|km|mi|abbr=on}} "light haze" smokescreen around the harbour throughout daylight hours, for two months. The density of this screen was adjusted to be sufficient to prevent observation by German forward observers in the surrounding hills, yet not inhibit port operations.

In the Vietnam War, "Smoke Ships" were introduced as part of a new Air Mobile Concept to protect crew and man on the ground from small arms fire. In 1964 and 1965, the "Smoke Ship" was first employed by the [[145th Combat Aviation Battalion]] using the [[UH-1B]].<ref>{{cite web|url=http://www.118ahc.org/118thAHC.htm|title=118thAHC|website=www.118ahc.org}}</ref>

===Naval warfare===
[[File:USS Lexington (CV-2) steams through smoke screen 1929.jpg|thumb|{{USS|Lexington|CV-2}} obscured by a smoke screen, 1929]]
There are a number of early examples of using [[early thermal weapons|incendiary weapons]] at sea, such as [[Greek fire]], [[stink bomb|stinkpot]]s, [[fire ship]]s, and incendiaries on the decks of [[turtle ship]]s, which also had the effect of creating smoke. The naval smoke screen is often said to have been proposed by Sir [[Thomas Cochrane, 10th Earl of Dundonald|Thomas Cochrane]] in 1812, although Cochrane's proposal was as much an asphyxiant as an obscurant. It is not until the early twentieth century that there is clear evidence of deliberate use of large scale naval smokescreens as a major tactic.

During the [[American Civil War]], the first smoke screen was used by the ''[[CSS Robert E. Lee|R.E. Lee]]'', [[Blockade runner|running the blockade]] and escaping the {{USS|Iroquois|1859|6}}.

The use of smoke screens was common in the naval battles of [[World War I]] and [[World War II]].

==See also==
<!-- Please respect alphabetical order -->
* [[Early thermal weapons]]
* [[Military camouflage]]
* [[PT boat]]
* [[Smoke bomb]]

==References==
{{Reflist}}

==External links==
*{{Wiktionary-inline|smokescreen}}
*{{Commons category-inline|Smoke screens}}

{{Authority control}}

{{DEFAULTSORT:Smoke Screen}}
[[Category:Weapons countermeasures]]
[[Category:Smoke]]
[[Category:Sniper warfare tactics]]
[[Category:Diversionary tactics]]