The word flechette is French and means "dart" (literally, "little arrow"). It is a projectile having the form of a small metal dart, usually steel, with a sharp-pointed tip and a tail with several vanes to stabilize it during flight.

Bulk use

Flechettes were used as an air-dropped weapon in World War I. These were about four inches long and weighed a couple of ounces. Dropped from an airplane over enemy trenches, these gravity missiles were capable of penetrating a helmet and the wearer's skull.

Smaller flechettes were used in special artillery shells called "beehive" rounds (so named for the very distinctive whistling buzz made by thousands of flechettes flying downrange at supersonic speeds) and intended for use against troops in the open. They were used in the Vietnam War by artillery gunners to defend their positions against infantry attacks. Numerous treaties now forbid their use.

Heavy flechettes

These anti-tank rounds can be more effective than high explosive devices; see kinetic energy penetrators. For reasons why a smaller diameter projectile is desirable, see external ballistics and terminal ballistics.

Small arms ammunition

In the 1960s the U.S. Army began early developmental work on a flechette rifle cartridge. It fired steel darts that looked very much like steel nails with fins stamped into the back. The flechettes were 3–5 cm long, and 1–2 mm in diameter, with a 4–5 mm fin diameter. It was never fielded. Intermittent attempts have been made to develop a selective-fire flechette [[1]] several time since, with mixed results. There were also experimental flechette rounds for the M203 grenade launcher and the 12-gauge shotgun, but the military eventually decided that standard buckshot worked best in both.

Flechette rounds were developed for small arms for a number of reasons. Being very small and light compared to traditional jacketed lead or steel bullets, flechette ammunition weighs less per round, and thus an infantryman can carry more. Second is the issue of recoil--for the same amount of kinetic energy, a lighter bullet (with a higher muzzle velocity) produces less recoil, and thus less shot dispersion in automatic fire. The last reason was the emergence of lightweight, flexible body armor for the average infantryman. A very high velocity, small diameter projectile is able to easily penetrate body armor.

However, the flechette has a number of weaknesses that limit its effectiveness as small arms ammunition. They tended to penetrate heavy armor less effectively than heavier, higher momentum rifle bullets. Their extreme light weight caused them to be deflected extremely easily; a single leaf, or even a raindrop, could destabilize a flechette and cause it to tumble wildly. Because of the hard nature of the flechette, it does not deform on impact, and while it penetrates extremely well, it produces very little tissue damage. Since the purpose of firing at an opponent is to disable them, either by wounding or fear of wounding, having a projectile that does not cause major wounds is counterproductive. The last issue with small arms flechettes is accuracy. To fire the finned flechette out of a smoothbore requires the use of a sabot. Since flechettes do not work well when spun by rifling, the only source of stabilization is the fins. When the sabot separates, it can disturb the effectively unstabilized flechette, and cause deviations in its flight.

An interesting variation of the flechette that addresses its difficulties is the SCIMTR, developed as part of the CAWS project.