Smoke-screen
From Biocrawler, the free encyclopedia.
A smoke-screen is a release of smoke in order to mask the movement or location of military units such as infantry, tanks or ships.
It is most commonly deployed in a canister, usually as a grenade. The grenade releases a very dense cloud of smoke designed to fill the surrounding area even in light wind. They have also been used by ships.
Whereas smokescreens would originally have been 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 also available for vehicles is a superdense form used to prevent laser beams of enemy target designators or range finders on vehicles.
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Technology
Smoke grenades
These are canister-type grenades used as a ground-to-ground or ground-to-air signaling device. The body consists of a sheet steel cylinder with a few emission holes on top and at the bottom to allow smoke release when the grenade is ignited. The filler consists of 250 to 350 grams of colored (red, green, yellow or violet) smoke mixture (mostly potassium chlorate, lactose and a dye). Another type of smoke grenades, are the bursting kind. These are filled with white phosphorus (WP), which are 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). These double as incendiary grenades.
Smoke shell
See also Smoke shells.
Artillery and mortars 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 or bursting rounds.
Smoke generators
Very large or sustained smoke screens are produced by a smoke generator. This is a machine which heats a volatile material (typically oil or an oil based mixture) to evaporate it, then mixes the vapour 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 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—especially if a number of generators are used—the screen can build up to a considerable size.
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.
Naval methods
Warships have sometimes used a simple variation of the smoke generator, by injecting fuel oil directly into the smoke stack. They also use large floating smoke canisters, known as smoke buoys. In the past they have also used sprays of chemicals that fume on contact with air, such as titanium tetrachloride.
Tactics
Land fighting
Smoke-screens are usually used by infantry to cover movement in areas of exposure to enemy fire, they can also be used by armoured fighting vehicles, such as tanks, to cover a withdrawal.
For the crossing of the Dnieper river in October 1943, the Red Army laid a smokescreen 30 kilometres (18 miles) long. At the Anzio beachhead in 1944, US Chemical Corps troops maintained a 25 km (15 mile) "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.
Notable uses of smoke-screens in naval warfare
There are a number of early examples of using incendiary weapons at sea, such as Greek fire, stinkpots, fire ships, and incendiaries on the decks of turtle ships, which also had the effect of creating smoke. The naval smokescreen is often said to have been proposed by Sir Thomas Cochrane in 1812, although Sir Cochrane's proposal was as much an asphyxiant as an obscurant. Notably deliberate smokescreens were not used at the Battle of Tsushima. It is not until the early twentieth century that we get clear evidence of deliberate use of large scale naval smokescreens as a major tactic.
Smoke-screens were used during the Battle of Jutland in World War I.
In the Battle of the River Plate in World War II, the German pocket battleship Admiral Graf Spee used a smoke-screen to escape from the British cruisers.
In the Second Battle of the Atlantic in World War II, smoke screens were used by Allied destroyer escorts to mask the presence of the merchant ships from German U-boats.
