On 7 December 1941, USS Cassin was in the Pearl Harbor Navy Yard's Drydock Number One. She was supported on blocks alongside USS Downes (DD-375), as both destroyers underwent modernization work to better suit them for contemporary combat conditions. That morning's Japanese air attack left both of them as ruined hulks. Some bombs hit them and fragments from others punctured their fuel oil tanks. The resulting fire badly damaged their structure, and, when the dry dock was flooded, Cassin lifted off the keel blocks and fell over against Downes. The explosion of ammunition and of a torpedo on Downes produced further major damage. By the time the fires were put out later on 7 December, the two ships were essentially wrecked beyond repair, with their hulls bent out of shape, plating wrinkled by heat and poked full of holes by explosion fragments.