Is it ensure, insure, or assure?
cannon charge consisting of small round balls, usually of lead or iron, and used primarily as an antipersonnel weapon. Typically, the small iron balls were held in clusters of three by iron rings and combined in three tiers by cast-iron plates and a central connecting rod. This assembly, which reminded gunners of a cluster of grapes (hence the name), broke up when the gun was fired, spread out in flight like a shotgun charge, and sprayed the target area. Grapeshot was widely used in wars of the 18th and 19th centuries at short range against massed troops.