Systems and methods described herein provide for the protection of personnel within vehicles and structures from handheld grenades and other threats. According to one aspect of the disclosure provided herein, a countermeasure system includes an expandable countermeasure having a flexible body with a number of weighted projectiles attached around a perimeter of the body. A threat detection and launch control system detects incoming threats and, in response, triggers a launch of the expandable countermeasure from the launcher to intercept and neutralize the threat.