Helsinki's air defenses prioritized stopping bombers from reaching the city over the destruction of air targets. In a special type of barrage, several batteries would fire a wall of flak in front of the approaching bombers in an attempt to scare them into dropping their payloads too early and breaking away. AA shells had been jury-rigged by drilling the fuze-hole larger and filling the extra space with magnesium mixed with aluminium, turning their explosion from a dull red to a searing white.