The battleship should have been declared obsolete in 1921. However, for many complex reasons, the Navy decided to consider the test either invalid or a fluke. But history never forgets: World War II may have definitively proved that battleships and other big-gun surface warships were no longer the dominant naval weapons, but the battleship’s days were numbered well before the start of the war.
In a high-profile test that culminated on July 21, 1921, aviators led by Brig. Gen. William “Billy” Mitchell sank three captured German warships — demonstrating once and for all the advantage that aircraft have against warships.
The test embarrassed the Navy and its significance was hotly debated, making it one of the earliest examples of US military inter-service rivalry. It was also a glimpse of the tactics that would transform naval warfare over the following decades.
Battleships vs. airpower
After HMS Dreadnought entered service in 1906, battleships were considered the sovereigns of the seas. As military aviation matured, some believed aircraft were bound to play a larger role in combat at sea — including Mitchell, an airpower advocate.
A distinguished pilot who proved his command skills and the utility of airpower at the Battle of St. Mihiel in 1918, Mitchell wanted the US military to have an independent flying branch. (He is now considered the father of the US Air Force.)
Mitchell also argued that aircraft were better suited to defend US coasts than battleships, which he believed were prohibitively expensive. For the same price, Mitchell said, the Army could buy hundreds or thousands of aircraft that could swarm and sink enemy battleships — something aircraft had never actually done before.
To defend its role and its shipbuilding plans, the Navy tried to refute Mitchell with its own test on USS Indiana, a battleship built in the 1890s.
Indiana sunk after being hit repeatedly during the test in November 1920, but it was later revealed that the Navy dropped dummy bombs filled with sand and detonated explosives separately to sink the ship.
A year later, Mitchell was assistant chief of the US Army Air Service — the precursor to the US Army Air Corps — and took his arguments to Congress.
“All we want to do is to have you gentlemen watch us attack a battleship,” he said at a hearing in January 1921. “Give us the warships to attack, and come watch it.”
After much pressure and publicity, the Navy begrudgingly agreed to a joint Army-Navy test, dubbed Project B. Four captured German warships and the obsolete battleship USS Iowa would be used as target ships for Army and Navy S.E.5 fighters, F5Ls flying boats, and NBS-1 and Handley Page O/400 bombers.
The Navy set a number of odd conditions, seemingly to ensure the test’s failure.
The aircraft couldn’t use torpedoes, could only use certain bomb loads on each mission, and were only allowed two direct hits with their 1,100-pound bombs. Inspections would be conducted between bombing runs, and the ships also had to be sunk some 50 miles from the Virginia Capes, limiting the time the aircraft could spend in the target area.
Mitchell’s 1st Provisional Air Brigade was undeterred. The unit trained to drop its bombs around the ships instead of on them, believing that the water would magnify the shockwaves. The Air Service also prepared a batch of 2,000-pound bombs for the test.
The Navy conducted the first test on June 21, when 12 bombs from Navy F5Ls sank the submarine U-117. The next test, on June 29, saw Navy aircraft drop 80 dummy bombs on the Iowa. Only two found their mark, bolstering beliefs that no battleship could be sunk from the air.
On July 13, Mitchell’s unit finally took part, attacking the destroyer SMS G-102. S.E.5 fighters first conducted strafing runs, hitting the deck 25 times with 25-pound bombs to demonstrate that they could clear a ship’s deck of sailors and anti-aircraft weapons. Then, 16 NBS-1 bombers dropped 32 300-pound bombs, making four making direct hits and sinking the destroyer in 19 minutes.
Because G-102 was a small ship, sinking it with bombs wasn’t considered a groundbreaking accomplishment. Five days later, however, Mitchell’s unit sank the SMS Frankfurt, a modern light cruiser, with 600-pound bombs.
The coup de grâce came on July 20. As high-ranking observers looked on, the modern battleship SMS Ostfriesland was attacked by Army and Navy aircraft. Multiple hits by 230- and 600-pound bombs did little damage to Ostfriesland’s superstructure, but near-misses damaged its hull and caused it to list five degrees to port.
The test was paused because of a storm, but the next morning Army NBS-1 bombers scored three direct hits with 1,100-pound bombs. The Navy ordered a halt to assess the damage, preventing Mitchell’s men from finishing off the battleship. A few hours later, the bombers returned with 2,000-pound bombs.
To prevent the Navy from stopping the test again, Mitchell ordered his men to drop the bombs in the water close to the Ostfriesland instead of on the ship itself. Three of the six bombs detonated close enough to rip holes in the hull. Twenty-two minutes later, the battleship rolled over and sank.
Project B proved Mitchell’s argument that modern battleships could be sunk by aircraft. The Navy disputed its relevance, arguing that Mitchell’s aircraft had sunk stationary ships that had no active defenses and needed considerable resources to do it.
A joint Army-Navy Board report a month after the test said battleships were still “the backbone of the fleet and the bulwark of the nation’s sea defense” and would be so as long as “safe navigation of the sea” was required for commerce and conflict.
The sinking of the battleship USS Alabama in a similar test in September didn’t change any minds, and the 1st Provisional Air Brigade was subsequently disbanded.
Mitchell continued aggressively arguing his case for airpower and for an independent military flying branch. In 1923, he warned that the US naval base at Pearl Harbor was vulnerable to a Japanese air attack. His outspokenness led to his demotion and court martial in 1925.
Ultimately, World War II proved Mitchell correct about the transformative role of airpower in naval warfare — a role that only grew with technological advances during the war.
The British air attack on the Italian fleet at Taranto was a model for the Japanese attack on US ships at Pearl Harbor. British aircraft were also crucial to defeating the German battleships Bismarck and Tirpitz.
Even Japan’s Yamato and Musashi, the largest and most powerful battleships ever built, could not defend themselves from hundreds of aircraft committed to their destruction.
Benjamin Brimelow is a reporter at Business Insider, where this first appeared.