Capsizing of the USS Oklahoma
The USS California's salvage report indicates that two torpedoes hit the ship, in addition to bomb damage. After inspecting the hull in drydock, the report concluded that both torpedoes were "under 500 pounds and possibly as low as about 337 pounds."
The USS Nevada's salvage report indicates that one torpedo hit the ship, in addition to bomb damage. After inspecting the hull in drydock, the report concluded that "the damage to NEVADA is certainly indicative of a comparatively small charge...[and] suggests that aerial torpedoes carrying somewhat less than 500 lbs. of explosive have been used...."
Photos of the damage to both California and Nevada were used as a baseline against which other damage could be compared.
Possible torpedo damage to the USS Arizona is covered in another article on this website.
The remaining two ships from Battleship Row to suffer torpedo damage, USS West Virginia and Oklahoma, received the brunt of the aerial onslaught. Due to the extent of the damage, it was difficult to define exactly how many torpedoes hit, and where. We looked through the damage reports and accompanying photographs of each in drydock to look for evidence of any explosive damage more severe than the norm.
West Virginia's damage report
Starting with the USS West Virginia's War Damage Report, Rear Admiral Furlong, Commandant of the Navy Yard, estimated that four torpedoes struck the ship's armour belt (leaving "distinct imprints"), another "penetrated above the armor belt and exploded on the second deck", and another hit and blew off the rudder. The torpedo hitting above the armour belt must have been the last, hitting higher than usual after the port side of the ship had rolled and settled lower in the water by several feet. No estimate was given of the explosive size of the torpedo warheads, so we had to rely upon photos of the hull in drydock to assess the extent of the damage.
Most of the damage to "WeeVee" was concentrated amidships. Even though a number of armour plates in this area were fractured or warped and required subsequent replacement, the overall integrity of the armour belt withstood the multiple torpedo hits; in fact, the salvage report states that "the armor belt was found to be badly askew but nevertheless furnished excellent backing for shores [to install cofferdam patches in preparation for re-floating the vessel]."
In the following two photographs, it can be seen by looking down the length of West Virginia's armour belt that the belt was dented, but not broken, by torpedo hits.
Our conclusion, after comparing the text and photos from the West Virginia's damage report to those of California and Nevada, was that the damage to West Virginia was consistent with the aerial-dropped Type 91 Mod 2 torpedo. We just did not see in West Virginia the more extensive damage that we expect to have been caused by a submarine-launched Type 97 torpedo.