The U.S. Navy's Bureau of Ships put forward two hypothetical possibilities for the magazine explosion in the Arizona. Although neither of these scenarios was conclusive, they are part of the historical record. Bureau investigators based the first on film footage that captured a large visible flame fronting turret number one a half-second before the magazine explosion. They speculated that a bomb hit the forward aviation fuel tank, located near the bow of the ship, and caused a large fire forward of turret number one. The fire then set off the 14-inch powder magazine. The problem with this theory is that no evidence of external hull expansion or damage on the outer shell plating above the fuel tank storage area could be found to indicate such an explosion. Furthermore, the distance between the fuel tank and the powder rooms was 92 feet. At approximately half this distance, 44 feet aft of the fuel tank, a 13-inch-thick steel transverse bulkhead protected the ship's vital areas from any forward blast or hit. This armored front end bulkhead would have prevented a forward explosion from passing aft into the powder rooms.
Another early explanation hypothesized that hot debris from a bomb that exploded over the Arizona's armored deck found its way through an open hatch and into the powder storage spaces below, between the two forward turrets. This space below the armored deck may have contained highly flammable black powder that exploded and set off the surrounding magazines. For two reasons, however, this interpretation is highly unlikely. Black powder ignition charges to ignite the silk cordite bags had been replaced by newer technology. The newly loaded cordite bags contained black powder starters within the bag lining and eliminated the need for extra black powder charges to be stored. This second explanation also assumed that with a ten minute alarm, the men were not at battle stations, and therefore, the hatches leading to the magazine spaces below were not in condition Z (all doors and hatches closed). The men in the aft main battery turrets, however, were in condition Z before the explosion occurred. This explanation also wrongly assumed that the Japanese bomb did not have the potential to penetrate the battleship's armored deck.
Although original damage reports on the Arizona listed as many as eight bomb hits, Japanese aviators estimated as many as four. The lower Japanese account is far more realistic. And now, with the addition of new data, the official Japanese testimony of four hits can be lowered to only two hits and two very near misses.
Using Japanese information on "vee" bomb impact points, investigators developed a simple, computer-generated graphic model to help determine the No. 80 bomb points of impact (see Bomb Impact Overlay). By placing the overlay over reconstructed silhouettes of the moored USS Vestal (AR-4) and the Arizona, impact points become apparent, and they match documented bomb hits on the Vestal, moored outboard the Arizona, splash points between the ships, and two reported impact points on the Arizona herself.
Of great interest were the two points where No. 80 bombs hit the water between the two ships. Surprisingly, several reports indicated torpedo detonations in the same two areas. One important report of a splash between the Vestal and the Arizona came from Commander Cassin Young, skipper of the Vestal, who thought a torpedo detonation caused the splash. Young noted that the splash occurred near frame 35 on the Arizona. He and a number of his crew witnessed and correctly reported that a bomb hit the Arizona's forecastle at the same time as the outboard splash occurred. The report also stated that the magazine exploded a short time later. Japanese photographic evidence and air records, however, clearly discount any possibility of a torpedo attack on either ship. The reported splashes between the ships can be attributed only to No. 80 bombs dropped from the high-level bombers.
Further evidence debunking the reported torpedo hits on the Arizona came from the U.S. Navy. In 1942, the Navy conducted an underwater excavation of the entire forward section of the Arizona's hull, below the mud line. Navy divers, using high-pressure water jet hoses, removed the mud from the sunken forward half of the ship to a point ten feet beyond the turn of the bilge and found no evidence of a torpedo hit. Furthermore, the Vestal received no hull damage that would have been expected from any nearby torpedo detonation.
Motion picture film further corroborated the already collected bomb impact evidence. Black-and-white footage of the Arizona's final seconds captured a single bomb splash on the Ford Island side of the battleship near mooring quay F-7. Again, this splash fit into the computer-generated overlay of predicted "vee" impact points. The vee bomb pattern also predicted a bomb hit on the stern half of the Vestal. Surprisingly, the Vestal's damage report stated that she received a bomb hit aft and that the bomb passed completely through the ship at frame 110. This stern hit matched the other No. 80 impact point. With four known impact sites identified, evidence called for reconstructing the entire five-bomb vee impact pattern.
The same computer-generated image of vee-bomb impact points also helped to eliminate the wartime speculation of bomb hits in the midships area. No bomb patterns matched to support wartime U.S. Navy reports of hits on the Arizona's midships section. This is especially important because of the many statements that a bomb went down her smokestack. No evidence of bomb penetration on the smokestack's armored grill could be found. Furthermore, live U.S. film footage taken at the time of the Arizona's magazine explosion clearly showed that the blast occurred forward, before any smoke vented out of the smokestack.
Many other small holes and gouged-out areas on the Arizona's midships area can be attributed only to the explosion of the forward magazine and to the cooking off of numerous 5-inch shells by the ensuing fire. This includes gutted and mangled areas that extended some 60 feet across the boat deck area aft of the collapsed bridge. The forward collapse of the bridge caused the large topside tear.
The Japanese No. 80 bomb's penetrating ability must be called into question. Did it have the potential to penetrate a 5-inch armored deck and the 1-inch protective deck over the powder room? Japanese documents emphatically stated that the No. 80 bomb could penetrate 5.9 inches of German-manufactured armor (MNC) plate, when the bomb was dropped from a height of 8,200 feet. The No. 80 bomb that hit the Arizona's forecastle was released 2,300 feet higher and would have had a penetrating potential nearing 7 inches of steel plate. The No. 80 also was an armor-piercing weapon with a small bursting charge of 50 pounds. This bomb characteristically left a small entry hole approximately 24 inches long and 20 inches wide in topside decks and penetrated deep into the bowels of the target ship.
Given the evidence, a conclusive picture emerges of the Arizona's last minutes. The Arizona and the Vestal each suffered two No. 80 bomb hits from the carrier Kaga's high-level bomber group at 0805. Lieutenant Hideo Maki's group scored one hit on the Arizona's number-four turret (frame 119) and one hit on the Vestal's starboard side near the ship's bow at frame 44. The bomb that struck the Arizona hit the number-four turret, glanced off the sloping armor plate near the turret's face, and was deflected aft, passing below deck, exploding in the flag officers' pantry, causing only minor damage to the ship. The bomb that struck the Vestal at frame 44 passed through three decks, entered the pipe storage area, and deflected toward the bow before exploding, causing a fire but no flooding. Three other bombs missed both ships.
A minute after the first attack, a second group of high-level bombers under the command of Lieutenant Commander Tadashi Kusumi from the aircraft carrier Hiryu, loaded with No. 80s, attacked the damaged Arizona and Vestal. At approximately 0806, the Hiryu group target acquisition bomber flying in the point selected a battleship target. Using a small, white, rectangular flag, the lead target-acquiring bomber signaled the four others to release their bombs. Lieutenant Commander Kusumi's bombardier, Lieutenant Shojiro Kondo, released the fateful bomb that destroyed the Arizona from 3,200 meters (10,480 feet) with an expected impact time at a fraction more than 26 seconds. At this elevation, the bomb's double fuses were set to detonate under the ship's bottom. Like the earlier high-level bomber formation, Kusumi's group scored one hit on the Arizona and one hit on the nearby Vestal. The bomb that hit the Vestal struck on the port side at frame 111 and passed completely through the ship. Whether this bomb detonated or passed into the mud on the harbor's bottom remains unclear, but nonetheless, this hit caused extensive flooding in the aft sections of the ship. The Vestal was later pushed into the shallows of the harbor and beached to prevent her from sinking.
Now, the final seven seconds of the Arizona come more sharply into focus. The ship had six powder rooms for her 14-inch guns, three on either side of the two forward 14inch main turrets. The lethal bomb struck the starboard side of the forecastle deck, adjacent to turret number two. The No. 80 bomb passed through four decks and 5.62 inches of armor before touching off the powder magazine. The first flash occurred in the powder room on the starboard side of the number two turret handling room (see Magazine Explosion Illustration). Two neighboring powder rooms were just forward of this flash point. Expanding gas from the first powder room to be hit spread forward to the two adjacent powder rooms. Gas quickly filled the starboard voids below the armored deck and spread forward to the 13-inch-thick armored end bulkhead, which ran below the front edge of the armored deck forward of turret one. This front end armored bulkhead capped the forward ends of the 13.5-inch armored belt located on either side of the battleship's waterline.
The forward rush of super-heated gases smashed into the 13-inch armored wall of the front end armored bulkhead. The hot exploding gases then deflected upward through three decks and caused the fire-burst visible on the forecastle deck in front of turret number one. This brief burst of fire, which lasted only a half-second prior to the ensuing gigantic explosion, was an important clue captured by a movie camera on board the nearby hospital ship Solace (AH-5).
As the erupting gases broke through the decks forward of turret one, the remaining 14-inch powder magazine rooms on the port side ignited. With all forward and starboard voids below deck already filled with expanding gases, super-heated gases from the port-side powder rooms could vent only outward, upward, and forward. The result was a catastrophic explosion that broke through the remaining horizontal structures and the hull plating above the armored belt. Witnesses felt and saw the blast for miles around the harbor. Approximately 582 tons of 14-inch ordnance stored in the forward magazine area were consumed by the blast. Film footage captured the entire external process, from the bomb hit to the final explosion. The whole process took slightly less than seven seconds. The Arizona's bridge collapsed forward into the flaming cavity, and she sank within nine minutes. The devastation to the forward third of the ship was so massive that salvage divers during the war found only one spent 14-inch powder can out of more than 1,000 stored in the forward powder rooms. In 1984, the National Park Service's Submerged Cultural Resource team, led by Daniel J. Lenihan, conducted a comprehensive underwater survey of the Arizona's wreck. During this time, one Park Service discovery of particular interest was the charting of unusual hull distortions outside and on either side of the forward magazine. In the area of the forward magazine, the outer hull portion on the port side bulged outward far more than the starboard side.
The greater port hull distortion provided a historical steel fingerprint and testimony to the final seconds of the Arizona. The greater outward distortion on the port side provided evidence that the starboard powder magazines ignited first. With all the surrounding voids already filled by super hot expanding gases, the later exploding cordite in the port magazine was forced to vent outward more on the port side of the hull. This caused a greater hull displacement on the port side. Further evidence of the greater port side outward distortion is a large crack found on the outer shell plating that extends down to the turn of the bilge and possibly beyond. Park Service diving specialist Jim Adams confirms that this crack can be found only on the port side and not on the starboard side of the hull.
The sequence of events, starting from the second bomb's release point to the explosion of the forward magazine, took no more than 33 seconds. The tragic loss of the Arizona ended the era of battleship supremacy and gave rise to the new master of the oceans, the aircraft carrier.