During a mine countermeasures demonstration, a 55-gallon drum was placed at the base of a bridge stanchion to simulate an underwater improvised explosive device/mine. The new object identified in the "After" sonar imagery above is the 55-gallon drum. A drum of this size filled with explosives and a detonating mechanism would be enough to destroy the stanchion resulting in bridge collapse. Using methods of change detection as illustrated in the animation, underwater threats can be identified for engagement and neutralization.