The degraded chemical weapons were first discovered in May 2004, when a binary sarin nerve gas shell was used in an improvised explosive device (roadside bomb) in Iraq. The device exploded before it could be disarmed, and two soldiers displayed symptoms of minor sarin exposure. The 155 mm shell was unmarked and rigged as if it were a normal high-explosive shell, indicating that the insurgents who placed the device did not know it contained nerve gas. Earlier in the month, a shell containing mustard gas was found abandoned in the median of a road in Baghdad.