Igniting the Mystery
The attack on Pearl Harbor, which occurred on the 7th December 1941, stands as one of the pivotal moments in U.S. history.
One of the most enduring symbols of this tragedy is the destruction of the USS Arizona (BB-39), where 1,177 U.S. Navy personnel lost their lives.
The ship's destruction was so devastating that it continues to be a powerful representation of the Pearl Harbor attack and the subsequent entry of the United States into the Second World War.
Yet, despite its historical significance, much of the exact nature of how the Arizona was sunk remained unclear for decades.
Over time, researchers have gradually pieced together the factors contributing to the massive explosion that ripped the ship apart, especially in the wake of the attack.
A Mighty Deterrent
The USS Arizona (BB-39) was a Pennsylvania-class battleship, launched in 1915 and commissioned in 1916, representing the U.S. Navy's growing naval power during the early 20th century.
Named after the 48th state to join the Union, the Arizona was designed for power and endurance, with twelve 14-inch guns and strong armor.
Although completed too late to serve in the First World War, the battleship played a key role in projecting American naval strength during the interwar period.
Arizona's launch, 19 June 1915
...helping maintain U.S. presence and influence in the Pacific...
In the 1920s and 1930s, the Arizona served in various capacities, primarily with the Pacific Fleet.
She participated in fleet exercises, training missions, and goodwill visits, helping maintain U.S. presence and influence in the Pacific and beyond.
The ship underwent significant upgrades in the 1930s, including the addition of anti-aircraft guns and improvements to armor and fire control systems.
USS Arizona. Underway during the 1930s.
...these measures alone would be insufficient against the overwhelming air attacks...
However, despite their power, the Pennsylvania-class battleships had a maximum speed of only 21 knots, making them slower than more modern battleships and vulnerable to faster enemies, particularly aircraft carriers and their aircraft.
By 1941, naval combat had shifted toward air superiority, and these battleships could not easily evade air attacks.
Furthermore, the battleships were designed before the full advent of naval aviation and although they were upgraded with additional anti-aircraft guns, these measures alone would be insufficient against the overwhelming air attacks that became common in the Second World War.
The USS Arizona in 1934.
...a symbol of U.S. naval supremacy...
By 1940, as tensions with Japan escalated, the Arizona was stationed at Pearl Harbor as part of the Pacific Fleet's deterrent against Japanese aggression.
Along with other battleships, she was seen as a symbol of U.S. naval supremacy.
Prior to the attack on December 7, 1941, the Arizona was in port undergoing maintenance and routine readiness drills, unaware of the imminent assault that would mark her final moments.
Target Arizona
On the 7th December 1941, the Imperial Japanese Navy launched a surprise attack on Pearl Harbor, targeting the U.S. Pacific Fleet.
The USS Arizona (BB-39), a Pennsylvania-class battleship, was moored at Battleship Row during the early hours of the assault.
At approximately 8:06 a.m., the Arizona was struck by an armor-piercing bomb dropped by a Japanese high-level bomber.
The bomb penetrated the deck near turret number two, passing through several decks before detonating in the forward powder magazine, which stored ammunition for the ship's 14-inch guns.
The forward magazines of USS Arizona (BB-39) explode after she was hit by a Japanese bomb, 7 December 1941. Frame clipped from a color motion picture taken from on board USS Solace (AH-5) (80-G-K-13513).
...the vessel quickly sank to the shallow harbor floor...
The explosion was catastrophic, causing a massive fireball and sending shockwaves through the harbor.
The forward third of the ship was completely destroyed in the blast, and the vessel quickly sank to the shallow harbor floor.
Flames engulfed the remains of the ship as oil and debris spread across the water. Nearby ships and personnel attempted to assist, but the devastation was too severe.
The USS Arizona exploding - a sequence of shots taken from colourised film footage captures the devastation inflicted upon the Battleship..
...adding to the chaotic scene...
The explosion on the Arizona resulted in the loss of 1,177 crew members.
Smoke from the fires could be seen from miles away, adding to the chaotic scene as Japanese planes continued to strafe the harbor.
Within minutes, the USS Arizona was a wrecked hulk, her hull broken and burning as the attack on Pearl Harbor continued throughout the morning, severely crippling the U.S. Pacific Fleet.
Simplistic representation of the explosion on Arizona.
https://www.rebellionresearch.com/the-bomb-that-sank-uss-arizona
Early Theories: Fuel tank or Open Hatch?
In the immediate aftermath of the attack, two prominent theories emerged from investigations conducted by the U.S. Navy’s Bureau of Ships.
These hypotheses were developed from observations, witness testimonies, and early footage of the attack.
The first theory postulated that a bomb hit near the forward aviation fuel tanks, located at the ship’s bow, causing a fire that ultimately set off the 14-inch powder magazine.
The second theory suggested that hot debris from a bomb that detonated over the Arizona's armored deck found its way through an open hatch into the ship's powder storage area.
However, both theories were incomplete and lacked definitive evidence to fully explain the catastrophic explosion.
...Investigators speculated that a bomb hit the forward aviation fuel tank...
The first hypothesis was based on observations from footage showing a flame in front of turret number one, moments before the explosion. Investigators speculated that a bomb hit the forward aviation fuel tank, located near the bow, causing a large fire that spread and set off the powder magazine.
However, this theory ran into several challenges. For instance, no evidence of external hull expansion or damage was found on the outer shell plating above the fuel tank, which would have indicated an explosion.
Additionally, the distance between the fuel tank and the powder rooms was significant—92 feet—and protected by a 13-inch-thick steel bulkhead.
This bulkhead would have shielded the ship’s vital areas from any forward explosion, making it highly unlikely that a fire near the bow could have traveled back to the powder magazine.
...hot debris found its way into an open hatch, igniting black powder in storage...
The second early hypothesis was equally problematic. Investigators suggested that a bomb exploded above the ship’s armored deck, and hot debris found its way into an open hatch, igniting black powder in storage.
This chain reaction would have led to a larger explosion that consumed the magazine.
However, by 1941, the Arizona had been upgraded with more modern technology, replacing black powder charges with silk cordite bags containing built-in black powder starters.
This would have reduced the amount of loose black powder stored on the ship.
Moreover, there was evidence that the hatches were in condition Z (all hatches closed) before the explosion occurred. Thus, the idea that hot debris could penetrate the magazine space through an open hatch was deemed implausible.
The wreck of the USS Arizona photographed on the 10th December 1941
National Archives and Records Administration
Japanese Bombing Patterns: A More Realistic Picture
While these initial theories had their flaws, further investigations began to shed light on the more likely cause of the explosion.
In recent years, researchers from the National Park Service, working alongside various historical and technical experts, have uncovered new evidence pointing to a different scenario.
Japanese air records, interviews with aviators, and bomb data helped reveal a clearer picture of the attack and the sequence of events that led to the *Arizona’s* destruction.
...no evidence of dive bombers targeting the ship...
Japanese air records indicate that only high-flying horizontal bombers struck the *Arizona* before her magazine exploded.
There is no evidence of dive bombers targeting the ship, nor is there any indication that torpedo bombers attacked the Arizona’s berth.
The primary targets of the initial wave of high-level bombers were battleships like the *Arizona* and her nearby companion, the repair ship USS Vestal.
...which proved to be the fatal blow...
The Arizona was struck by two bombs, both of which were armor-piercing No. 80 bombs, weighing 1,756 pounds each.
These bombs were dropped from high altitudes, with the Japanese records showing they were released from over 10,000 feet.
The Arizona suffered two hits: one on turret number four and the other near turret number two, which proved to be the fatal blow.
Bomb Impact and Penetration Analysis
A key factor in the destruction of the USS Arizona was the performance of the Japanese No. 80 armor-piercing bombs, which were specifically designed to penetrate the thick armor of warships.
According to Japanese military documents, these bombs could pierce up to 5.9 inches of armor plate when dropped from an altitude of 8,200 feet.
However, during the attack on Pearl Harbor, the bombs aimed at the Arizona were released from an even greater altitude—over 10,000 feet.
This increased altitude added significant kinetic energy to the bombs upon impact, boosting their penetration capability to approximately 7 inches of steel plate.
...main function was to penetrate deeply into enemy vessels...
The Arizona was struck by two No. 80 bombs, but the most devastating hit occurred near turret number two.
The bomb penetrated the ship's 5-inch-thick armored deck and continued through four additional decks before reaching the forward powder magazine.
The design of the No. 80 bomb was not focused on creating large surface explosions; it carried only 50 pounds of explosive material, which was relatively small.
Its main function was to penetrate deeply into enemy vessels, reaching critical internal spaces such as engine rooms or, in the case of the Arizona, the powder magazine.
...precision and destructive potential of these bombs marked a turning point in naval warfare...
Upon penetrating the magazine, the bomb’s detonation triggered a catastrophic chain reaction, igniting the cordite stored for the ship’s 14-inch guns.
This chain reaction led to the massive explosion that destroyed the forward third of the battleship.
The explosive power of the magazine, combined with the ship’s design to store large quantities of ammunition, amplified the damage, resulting in the Arizona sinking in just nine minutes and the loss of 1,177 lives.
The precision and destructive potential of these bombs marked a turning point in naval warfare, underscoring the vulnerability of even heavily armored battleships to air-delivered bombs.
New Technological Insights: Computer-Generated Models and Film Analysis
In addition to the analysis of Japanese bombing records, advancements in modern technology have enabled researchers to refine their understanding of the USS Arizona's destruction.
One of the key breakthroughs has been the use of computer-generated models, which allow investigators to simulate the dynamics of bomb impacts and the resulting explosions.
These models integrate data from both Japanese and U.S. sources, including aviation records, damage reports, and underwater surveys.
By doing so, researchers can visualize and analyze the exact points where the bombs hit the Arizona and the nearby repair ship, USS Vestal.
...these findings matched precisely with Japanese records...
The use of digital modeling has been instrumental in discrediting several long-held myths, such as the belief that a bomb went down the Arizona’s smokestack or that the ship was hit midships.
When bomb impact points were superimposed onto a digital reconstruction of the moored Arizona and Vestal, it became clear that two bombs struck the Arizona—one near turret number four and the fatal hit near turret number two.
Additionally, these findings matched precisely with Japanese records, which indicated that No. 80 armour-piercing bombs were responsible for the damage.
...a much clearer picture of the precise damage caused during the attack...
Furthermore, the computer models helped clarify damage to the Vestal, confirming that the ship was hit by one of the No. 80 bombs, which passed completely through its structure.
By combining bomb data with physical damage reports, researchers now have a much clearer picture of the precise damage caused during the attack, helping to refine the timeline and dynamics of the explosion that destroyed the Arizona.
This technological advancement has provided a more scientifically accurate understanding of the Pearl Harbor attack and the destruction of the Arizona, contributing valuable insights to naval history.
Debunking Theories
One persistent myth surrounding the Arizona’s sinking was the belief that torpedoes played a role in her destruction. This theory stemmed in part from an eyewitness account by Commander Cassin Young of the USS Vestal, a repair ship moored next to the Arizona.
Young reported seeing a splash near the Arizona, which he believed was caused by a torpedo. However, both Japanese air records and subsequent U.S. Navy underwater excavation efforts have debunked this claim.
Detailed underwater inspections of the Arizona’s hull, conducted after the attack, found no evidence of torpedo damage.
Instead, further analysis attributed the splash that Commander Young witnessed to bomb impacts between the two ships, likely caused by high-level bombers dropping their payloads near the Arizona.
...the intense heat and pressure, contributing to the ship's widespread destruction...
Similarly, the theory that a bomb went down the Arizona’s smokestack was also proven incorrect. This idea gained traction early on, but live footage of the ship's final moments clearly shows that the explosion originated forward of turret number one, far from the smokestack.
Investigations into the midships damage revealed that the destruction in this area was not the result of direct bomb hits, but rather the forward magazine explosion.
This massive blast caused a chain reaction, igniting 5-inch shells stored midships, which “cooked off” due to the intense heat and pressure, contributing to the ship's widespread destruction but not as a result of additional bomb strikes.
The Final Seven Seconds: Reconstructing the Magazine Explosion
With the impact points and bomb characteristics clearly identified, researchers turned their attention to the final moments before the Arizona's destruction.
The bomb that struck near turret number two ignited the ship’s forward powder magazine, which stored the 14-inch ordnance for her main guns.
The Arizona had six powder rooms for her 14-inch guns, three on each side of the two forward turrets.
The bomb penetrated the starboard side of the forecastle deck and passed through multiple decks before detonating in the magazine below turret number two.
...triggered a flash in the starboard powder room...
The explosion sequence was devastating. The bomb’s initial detonation triggered a flash in the starboard powder room, which spread rapidly to two adjacent powder rooms.
As the superheated gases expanded, they rushed forward to the armored bulkhead protecting turret number one.
The explosion was so powerful that it deflected upward, causing the visible fire burst captured in film footage, just moments before the final explosion.
...tons of ordnance were consumed in the blast...
As the explosion continued to spread, the remaining powder rooms on the port side of the ship ignited, adding to the destructive force.
The resulting blast tore through the ship’s structure, venting through the decks and hull plating. The explosion was so massive that it could be seen and felt miles away.
Approximately 582 tons of ordnance were consumed in the blast, and the forward third of the ship was completely destroyed. The bridge collapsed, and the Arizona sank within nine minutes.
Aftermath and Legacy
The destruction of the USS Arizona during the attack on Pearl Harbor marked a significant turning point in naval warfare, signaling the end of battleship dominance.
Once considered the backbone of naval fleets, battleships like the Arizona were heavily armored and designed to engage enemy warships in direct combat.
However, the Japanese bomb strike that ignited the Arizona’s powder magazine, causing a massive explosion, exposed the vulnerability of even the most well-armored battleships to aerial attacks.
This event, along with the damage inflicted on other battleships like the USS Oklahoma and USS West Virginia, demonstrated that battleships were no longer invulnerable in the face of airpower.
...underscored the importance of air superiority in naval engagements...
The shift in naval strategy became clear as aircraft carriers rose to prominence following Pearl Harbor.
The attack underscored the importance of air superiority in naval engagements, and during the Second World War, carriers like the USS Enterprise and USS Hornet became the centerpiece of the U.S. Navy's offensive power.
The Battle of Midway, fought just months after Pearl Harbor, highlighted this shift, as aircraft from U.S. carriers destroyed four Japanese carriers, marking a decisive victory that shaped the course of the war in the Pacific.
...a powerful reminder of the human cost of war...
Today, the USS Arizona remains a symbol of this change in naval warfare and a memorial to the 1,177 sailors who lost their lives during the attack.
The USS Arizona Memorial, built over the sunken battleship, serves as a powerful reminder of the human cost of war and the brave men who served aboard her.
The site continues to attract millions of visitors, honoring those who made the ultimate sacrifice during the Second World War.
Aerial view of the sunken USS Arizona.
https://www.warhistoryonline.com/instant-articles/discovering-arizona-sunken-ship.html
USS Arizona Memorial, Pearl Harbor, Hawaii.
https://www.warhistoryonline.com/instant-articles/discovering-arizona-sunken-ship.html
Conclusion
The theories surrounding the cause of the explosion that destroyed the USS Arizona have evolved significantly since 1941. Early hypotheses, such as the forward aviation fuel tank explosion and the open hatch theory, have been largely debunked by more recent investigations.
Today, thanks to modern technology, computer-generated models, and historical data, a clearer picture has emerged. The primary cause of the Arizona’s destruction was the detonation of her forward powder magazine, triggered by a high-level Japanese bomb that penetrated the ship’s armored deck.
The explosion, which took no more than 33 seconds to unfold, was catastrophic, ending the lives of over 1,000 men and sinking the ship in minutes. This tragic event not only left an indelible mark on U.S. history but also symbolized the end of battleship supremacy and the rise of air power in naval warfare.
Further reading
