These projectiles, called fléchettes, are rarely seen or used in modern conflict, experts have said. Many landed in the street in the strike, Chmut said, including some observed by Washington Post reporters, among fields of gear and the occasional liquor bottle or chocolate bar abandoned by retreating Russian soldiers.

At 3 centimeters in length, these fléchettes look like tiny arrows. They have a long history in war — a version of them was dropped from airplanes in World War I and used by the U.S. in Vietnam — but are not in common use today. Shells packed with fléchettes are primed to explode over infantry formations and spew projectiles in a conical pattern, with some versions dispersing fléchettes across an area three football fields wide…

Fléchettes are narrowly shaped to achieve aerodynamic stability and with simple, nail-like manufacturing in mind, said Neil Gibson, a munitions expert at the U.K.-based Fenix Insights group. The fléchettes recovered from Chmut’s yard likely came from a 122 mm 3Sh1 artillery round, he said, which is among a few Russian munitions that carry the projectiles.