The Imperial Japanese Navy aircraft carrier Shinano was, at the time of its completion, the largest aircraft carrier in history to that point. It was heavily armored for a carrier, a 72,000-ton behemoth.
A behemoth that sank not only without sinking an enemy ship or engaging in a major battle, but that never even launched a plane.
The IJN Shinano was the largest aircraft carrier in history in 1944, but she was doomed to sink without ever launching a plane. (Photo: Marine engineer Hiroshi Arakawa, Public Domain)
On Dec. 7, 1941, Japan had a much larger and stronger fleet than the U.S. and early Japanese victories after Pearl Harbor made it seem undefeatable. But America's industrial might and intelligence breakthroughs allowed the U.S. to reverse the tides.
The tipping point came at the Battle of Midway when American forces sank four fleet carriers and a heavy cruiser.
The Imperial brass had to make tough decisions quickly to protect the Japanese Navy and regain the initiative. Admirals turned to a Yamato-class battleship still under construction, the Shinano, and made the decision to finish it as an aircraft carrier instead.
The USS Yorktown during the fierce air battle at Midway in 1942. The Yorktown was lost, but it helped sink three Japanese carriers. Japan also lost a fourth carrier and a cruiser in the battle. (Photo: U.S. Navy)
The Yamato-class battleships were the largest in history, greater even than the famed German Bismarck. But as American success had proven, the age of the battleship had closed and the age of the carrier had begun.
Converting the Shinano to a carrier took a lot of work and design compromises. The battleship armor was reduced but was still thicker than what most aircraft carriers boasted. Even the Japanese armored carrier Taiho got by with less.
The Japanese battleship Yamato was the largest in the world. One of its planned sister ships, the Shinano, was completed as an aircraft carrier. (Photo: Public Domain)
All the extra armor limited the Shinano's potential air fleet to 47 planes compared to the Taiho's 63 operational planes and 15 reserve spares. But the Shinano held lots of fuel and ammo and was expected to act as a support carrier, launching its own planes and resupplying all nearby aircraft during battle.
But that wasn't in the cards for the massive ship. It was launched on Oct. 8, 1944, and was sent from Yokosuka, Japan, to Kure, where it was scheduled to receive its aircraft.
On Nov. 29, 1944, the ship was hit by four torpedoes from the American submarine USS Archerfish. The Archerfish had been sent to the area to rescue aircrews downed during bombing runs on Tokyo, but began conducting normal patrols when the bombing missions were called off on Nov. 11.
The USS Archerfish sank the world's largest aircraft carrier with a single torpedo spread in 1944. (Photo: Public Domain)
The Archerfish first spotted the Shinano while surfaced at night on Nov. 28. A lookout reported seeing a large mass and the captain referenced his nautical charts and told the lookout that the mass was an island. The radar officer responded, "Captain, your island is moving."
The Shinano spotted the Archerfish following it and, probably suspecting that the sub was one member of a wolf pack, began zig-zagging across the water to avoid shots from other subs.
This was a mistake.
The Archerfish was alone and wouldn't have been able to catch the Shinano if it had fled or dispatched one of its destroyers to hunt the sub.
Instead, the carrier's evasive maneuvers allowed the sub to slowly get in range and launch a spread of 6 torpedoes over 40 seconds. Four of them smashed in the Shimano just above the carrier's thick anti-torpedo protections.
The USS Mississinewa sinking after being struck by a Keitan torpedo. World War II torpedoes punched massive holes in the sides of ships, allowing water to rush in and sometimes igniting fuel or exploding ammunition. (Photo: U.S. Navy)
The Japanese destroyers finally turned to fight and the Archerfish was forced to dive to avoid the depth charges that followed.
The torpedo damage to the Shimano caused it to slowly list. The Japanese captain attempted to flood the opposite side to keep the ship level, but the ship had rolled too far and the water inlets were exposed to the air. Unable to correct the list, the captain gave the order to abandon ship. It rolled and sank a few hours later.
The Archerfish was originally credited with sinking a light carrier. The Shimano's silhouette was unique, and U.S. naval intelligence had to make its best guess as to what sank. After the war, the Japanese acknowledged the battle and alerted the U.S. to the size of the ship they sank.
The Archerfish crew was awarded the Presidential Unit Citation. It was present in Tokyo Bay when the articles of surrender were signed on the deck of the USS Missouri on Sept. 2, 1945.