M18 smoke grenade
The M18 Colored Smoke Grenade is produced by the United States Army. Development began in 1942 after the Army Ground Forces requested a smoke hand grenade be made that had a visible range of 10,000 feet and could be used for marking friendly troop positions, identifying American tanks, or to signal location of downed planes. Utilizing previous experience in colored smoke signals, the Chemical Corps took on this task and had the first grenades designated "M16" available in April 1943. These grenades did not produce sufficient smoke for the Army Ground Forces, and so were remade shortly after production began. The redesigned grenades designated "M18" replaced the M16 and have been designated the standard issue colored smoke grenade for the United States Armed Forces since 24 September 1943.
Despite advancements in other methods used, colored smoke grenades are still regarded as a highly valuable communication method during military operations. They are primarily used for ground-to-ground or ground-to-air signaling, and target or landing zone marking.
Development History
Background
Prior to the creation of smoke grenades, basic colored smoke signals and flares were used by the United States Armed Forces. During World War I, American Expeditionary Forces operated in sectors held by the French Army. They used French and British equipment supplied to them, and observed that the French used red and yellow colored smoke signals. These smoke signals were used in a variety of formats such as on rockets with parachutes, rifle grenades, and in various calibers of pistol cartridges. After observing this, it was seen as beneficial to adopt the French Army system of pyrotechnics into the AEF in 1918. In the prior year, the Chemical Corps developed colored smoke signals for the AEF that came in colors of red, yellow, blue, green, and black. However, only yellow was produced at the time as dyes for the other colors were not available in the United States.After World War I, the research and development of various colored smoke munitions for the USAF increased. Colored smoke would eventually be available in bombs, mortars, canisters for various calibers of projectiles, and hand and rifle grenades.
Creation
In 1942, the Army Ground Forces requested a smoke hand grenade be made that had a visible range of 10,000 feet to be used for marking friendly troop positions, identifying American tanks, or to signal location of downed planes. Utilizing previous experience in colored smoke signals while cooperating with the Ordnance Department, the Chemical Corps took on this task. Development of colored smoke hand grenades began in September of that year.The initial problem that had to be figured out for creating the grenades was finding a mixture of chemicals that could produce smoke of desired color, volume, visibility, and duration while being heat-stable, commercially available, and inexpensive. Additionally the fuel used had to burn with sufficient intensity to volatilize but not destroy the dyes.
First models of the smoke grenades were based on the M7 tear gas grenade, utilizing its tube and fuse assembly. This was a -inches wide and -inches tall steel cylindrical tube with 3 lines of 6 emission holes going around the body. On top were 4 additional emission holes, and a threaded hole in the center that a M200A1 fuse went into. The fuel mixture chosen consisted of sulfur and potassium chlorate. Sodium bicarbonate was used as a coolant to absorb heat, helping the dye mixture burn longer while preventing it from decomposing. Organic dye mixtures that varied in composition based on color were pressed into the tube before the fuel mixture was added.
Finding the right dyes took time, with hundreds tested at the Edgewood Arsenal and various other agencies. Many were discarded due to not meeting visibility and color requirements, or for being in short supply at the time. Rather than the dyes being synthesized by Edgewood Arsenal Laboratories, they were obtained from various industries because of the variety and quantity required. Development was finished once all colors could be distinguished from 10,000 feet. These grenades produced smoke for 2 to minutes. They came in colors of red, orange, yellow, green, violet, and black and were designated as "M16" in April 1943, becoming standard issue and entering full production in May.
Shortly after the production of the M16 began, the Army Ground Forces tested its performance and decided they wanted a more rapidly burning smoke grenade with a denser smoke cloud. This was not possible with the current composition of fuel and dye mixtures and would result in the dyes burning rather than volatilizing. Proportions of ingredients in the mixtures were adjusted, along with the pressure at which they were compressed during production. The rows of holes around the tube the mixtures went into were removed, and a -inch hole was cut through the middle on the bottom.
The new grenades produced the desired denser, more vibrant colored smoke cloud, and had a shorter burning time of about 1 to minutes. They were designated as "M18" on 24 September 1943, entering full production and replacing the M16 which was then marked limited standard and stopped being produced.
Originally they were to come in the same colors as the M16, including white. During later testing it was decided that orange and yellow along with blue and violet were too similar for aircraft to differentiate from altitudes of 10,000 feet. Black and white were discarded because being able to identify them from other battle-field related smoke would be difficult. This left the M18 being produced in 4 colors instead which was red, yellow, green, and violet.
Subsequent Design Changes
In the 1950s the tube for the M18 was -inches wide and -inches tall. There were 6 emission holes on the top and an additional on the bottom covered by tape for smoke to release when ignited. On the top a M201A1 pull-ring fuse assembly was threaded into the middle, and the top was painted indicating the color of smoke inside. A yellow band and text painted on the body stated the color, lot number, and date produced following MIL-STD-1168 format.In the 1960s the M18 tube sized was changed to -inches wide and -inches tall. There were 4 emission holes on the top instead of 6, but the one on the bottom remained. The top was painted indicating the color, while the body came in gray or olive drab. A yellow or gray band and text were painted on the body. A waxed cardboard tube was used for shipping protection instead of metal.
In 2005, the top 4 emission holes were removed leaving only the bottom one. Inside the tube starter patches were put between pucks of dye during the manufacturing process to improve burning time and performance. The design was otherwise the same as the previous iteration.
Chemistry Changes
The smoke from an M18 is produced by volatilizing and condensing a colored dye mixture. The heat produced by the starter mixture volatilizes the dye which is then condensed by the air forming a colored smoke cloud. A cooling agent is added to the smoke mixture to help prevent excessive decomposition of the dye while burning time can be regulated by adjusting the amount of oxidant and combustible materials.During extensive testing with the M18 in the 1980s, it was found that the burning of the original chemical components resulted in a toxic smoke mixture so the formulas were remade.The new formulas used sugar for the starter mixture and magnesium carbonate as coolant. The dye mixtures were also changed, using different coloring components. The formula for the green and yellow M18 were changed quickly with relative ease, while red and violet were more challenging to produce. The sugar-based smoke compositions burned slightly hotter than the sulfur based ones, resulting in the dyes for red and violet burning instead of volatilizing. Additionally, it was also found the new violet smoke color mixture using Disperse Blue 3 even more toxic than the original. This was later changed to Disperse Red 11.
Due to the burning issues, red and violet M18's kept being produced using the original formulas until the early 2000s. They were then looked at again by the U.S. Army Environment Command and Environmental Security Technology Certification Program. They introduced wafer starter patches placed between dye pucks, which reduced the overall temperature during burning preventing the dyes from decomposing. The new red was found to produce a pinkish smoke rather than the intended darker red, caused by added Terephthalic Acid. Several attempts were made to correct it but were unsuccessful.
The new dye mixtures are produced by Nation Ford Chemical in South Carolina.
Old/New Mixture Comparison Table
Non-submersible Variant
In 1971, a non-submersible version of the M18 was created by Northrup Carolina, a subsidiary of Northrup Grumman at the time. This version was the same physical dimensions as the standard M18 and looked almost identical on the outside. The body contained a chimney design vent hole under the fuse assembly in the middle. Surrounding the chimney was a folded silicone fiberglass ballute that was attached to a bulkhead plate. 8 vent holes on the top of the bulkhead were used to inflate the ballute when the grenade was ignited. Below the bulkhead was a starter/ignition mixture, inflation mixture, and smoke mixture.When ignited and thrown, the top of the grenade with the fuse assembly detached while the ballute inflated. The grenade would then glide towards the ground upright, and could float in water. During testing it was found these versions of the M18 had a lower smoke volume but burning time was almost double of the standard M18 with 90 seconds minimum. Although testing was considered successful, this version of the M18 was not used outside of it. It was created as the standard M18 was found to provide poor visibility for signaling when used in areas partially or fully covered in water in Vietnam.