Some tactics make friendly fire virtually inevitable, such as the practice of dropping barrages of mortars on enemy machine gun posts in the final moments before capture. This practice continued throughout the 20th century since machine guns were first used in World War I. The high friendly fire risk has generally been accepted by troops since machine gun emplacements are tactically so valuable, and at the same time so dangerous that the attackers wanted them to be shelled, considering the shells far less deadly than the machine guns.