Flak was a projectile weapon that was often used by ground forces to attack aerial units. During the Clone Wars, the Confederacy of Independent Systems utilized Proton Cannons armed with flak cells as ammunition to defend their besieged worlds against Republic invasions, such as the second battle of Geonosis. It was also used by the Malevolence, the massive warship of General Grievous, in space battles to rip apart the enemy vessels.