Key point: She was not very seaworthy before her fateful encounter.
If weight alone could determine victory, then the Imperial Japanese Navy aircraft carrier Shinano might still be afloat.
At 69,000 tons when launched in 1944, the Shinano would have remained the world's largest aircraft until the 1960s. But that was not to be. Instead the Shinano earned a distinction of a different kind: the title of largest warship ever sunk by a submarine.
And the submarine that accomplished—the 1,500-ton USS Archerfish—was one-forty-sixth the size of its victim.
The story begins in May 1940, when the Shinano was laid down as the third of Japan's legendary Yamato-class battleships. These giants were the largest battleships in history, built as part of Japan's desperate attempt to counter U.S. naval quantity with a few—hopefully—qualitatively superior warships. If all went according to plan, the Shinano would join her sisters Yamato and Musashi as the three queens of Second World War battlewagons.
Yet by 1942, Japan began to realize that it needed aircraft carriers more than battleships. Naval warfare was now ruled by these floating airfields, and Japan had lost its four best at the Battle of Midway. The orders came down to convert Shinano into an aircraft carrier such as the world had never seen.
At 69,000 tons, it was the double the tonnage of the Essex-class carriers that won the Pacific War for America, and would remain the largest until the advent of nuclear-powered carriers in the early 1960s. Its main deck, already sheathed in armor up to 7.5 inches thick, became the hangar deck where aircraft were serviced. On top was the flight deck to launch and recover planes, itself protected by 3.75 inches of armor.