Abstract: An aircraft canopy breaking device, having means for penetrating the canopy lazing material upon application of an applied force from the rising ejection seat to the penetrating means. The device further comprises prepositioning means for prepositioning the penetrating means at a fixed distance from the canopy glazing material, shielding the penetrating means from inadvertently contacting the canopy glazing material, other material or personnel, and compressing whereby upon application of a force the penetrating means contacts the canopy glazing material causing crack propagation in the canopy glazing material.