Note 20 — Chapter III · ARRAS
Reading edition
These are used, generally in the ratio of one to four ordinary or armour-piercing bullets, to show the general direction in which the burst of fire is going. Instead of being filled with lead like the ordinary bullet, they contain phosphorus, which commences to burn as soon as the bullet is discharged from the machine gun, and leaves behind it a trail of smoke and fire to mark its course.