USS Pennsylvania, Cassin and Downes
When the Japanese raiders arrived over Pearl Harbor, the battleship Pennsylvania was in the Pearl Harbor Navy Yard's large drydock and therefore was beyond the reach of the torpedoes that inflicted such devastation on four of the fleet's other heavy ships. Though bombers of the second wave attacked her, Pennsylvania was directly hit only once, by a bomb that struck amidships, putting some of her five-inch guns out of action but generally causing only minor damage to the heavily-constructed ship.
Also in the drydock, side-by-side ahead of Pennsylvania, the destroyers Cassin and Downes were not nearly so lucky. Several bombs hit on or near them, puncturing their thin hulls with fragments, releasing fuel oil and starting major fires that badly strained their structure. They were further damaged by exploding ammunition and the detonation of one of Downes's torpedoes, which blew a large hole in her midships port side. Finally, when the drydock was partially flooded as a precaution against an attack on its entrance caisson, Cassin came partially afloat and capsized against her consort. The fires caused additional, but superficial, damage to Pennsylvania's bow, and the two destroyers were almost completely wrecked.
Initial impressions of the damage to USS Cassin were that she was a total loss, with salvage only necessary to clear Pearl Harbor's Drydock Number One, where she lay alongside the equally wrecked USS Downes (DD-375). However, closer examination showed that her main battery, hull fittings and machinery were in reasonably good condition. Accordingly, efforts soon began to remove guns and other topside equipment from the capsized ship, patch up her hull enough to allow it to float and turn her upright. Salvage work proceeded through January 1942 and into February as the drydock was periodically flooded to bring in or remove other damaged ships. Cassin was righted on 5 February and floated out of dock on the 18th. Her hull, wrecked beyond repair, was scrapped by October 1942, and the still-usable equipment was sent to the Mare Island Navy Yard for installation in a new hull.
Damage to USS Downes was so severe that she was initially thought to be only worth salvage to clear the drydock in which she rested alongside the capsized USS Cassin. However, it was soon found that the two ships' machinery, hull fittings and main battery guns could be repaired. During December 1941, efforts began to strip the ships of guns and other equipment and patch up their hulls to make them watertight enough to float. The salvable items would be shipped to the Mare Island Navy Yard for installation in new hulls, and the old hulls scrapped at Pearl Harbor. By 5 February 1942, work had progressed sufficiently to allow Cassin to be turned upright. A day later, Downes' remains were towed clear of the drydock for further work and eventual scrapping.