Unfortunately for officials in Tokyo, the Japanese Navy had struck a powerful blow, but not a crippling one. The bombardment failed to hit the repair facilities and fuel depots, which allowed the U.S. Pacific fleet to get back on its feet relatively quickly. Just as importantly, not a single U.S. aircraft carrier was in Pearl Harbor at the time. The flattops would swiftly prove their dominance over battleships in the coming Pacific War. Despite the debacle, the Japanese Navy continued sending Kō-hyōteki into combat. As at Pearl Harbor, the submariners in their tiny ships had very limited successes in operations from Australia to Alaska to Madagascar.
On Dec. 7, 1941, the aircraft of the Imperial Japanese Navy rained devastation upon the U.S. naval base at Pearl Harbor, Hawaii. But Japanese warplanes didn’t actually fire the first shots that brought America into a massive Pacific War.
An hour before the air attack, a squadron of tiny Japanese midget submarines attempted to slip into the harbor’s defenses, like burglars in the night, to wreak havoc on Battleship Row. Unlike the aerial assault, the sailors failed spectacularly — and the story is often forgotten.
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By the 1930s, Imperial Japan and the United States were set on a collision course. Tokyo’s decision to invade China in 1931 and intensify their brutal campaign six years had provoked ultimately irrevocable tensions.
The United States responded to the incursion into China with increasing sanctions, culminating with an embargo on petroleum in July 1941 that crippled the Japan’s economy. Japanese military leaders had wanted to capture the Dutch East Indies to secure its oil wealth, but knew it would trigger war with the Unites States.
While U.S.-Japanese negotiations came within striking distance of a peace agreement, Roosevelt was a hard bargainer, demanding Japan’s leaders order a complete withdrawal from China. They refused.
Thus, Japanese Adm. Yamamoto began planning for a “short victorious war.” The key to this idea was knocking out the battleships of the U.S. Pacific fleet at their home base of Pearl Harbor, Hawaii to buy the Japanese Army time to complete the conquest of the Western Pacific.
Along with a massive air strike from a Japanese carrier task force would constitute the main attack, the Navy coordinated the undersea assault using midget submarines.
During World War II, Japan, England, Italy and Germany all employed midget submarines to stealthily infiltrate shallow, defended harbors and attack vulnerable capital ships. The Japanese Navy’s midget submarines had hidden their developments by calling the ships Type A Kō-hyōteki , or “Target A”
Japanese officials hoped the designation would deceive foreign analysts into believing the 78-feet long submarines were actually mock ships for naval gunnery practice. In reality, each of the 46-ton subs had a crew of two and was armed with two 450-millimeter Type 97 torpedoes with 800 pound warheads.
The little submarines could sprint up to 26 miles per hour submerged, but could not dive deeper than 100 meters. More importantly, the Type As had no engine and ran purely on batteries.
This gave the diminutive vessels a maximum endurance of 12 hours at speeds of 6 miles per hour. The subs often ran out of power much faster in real combat.
As a result, a larger submarine mothership had to bring the Type As close to the target area. Even so, the battery limitations made it unlikely the midget sub could make it back to safety. Each one had a 300-pound scuttling charge as a self-destruct device.
Just getting to the designation was difficult enough. Since the small boats were difficult to control even while swimming in a straight line, crews had to manually move lead weights backwards and forwards to stabilize the vessel.
With these obvious issues, on Oct. 19, 1941, the Japanese Navy began modifying five Type A subs with improved pneumatic steering devices, as well as net-cutters and guards for fending off anti-submarine nets. Workers at the Kure Naval District painted over the submarine’s running lights to help hide them from enemy spotters.
Afterwards the midgets went to the Kamegakubi Naval Proving Ground and crews loaded them onto the backs of five large Type C-1 submarines, the I-16, I-18, I-20, I-22 and I-24. On Nov. 25, 1941, The motherships set sail for Pearl Harbor.
While on route, the so-called “Special Attack Unit” received the coded message “Climb Mount Niitaka 1208.” This meant authorities in Tokyo had not found a diplomatic solution and signaled the go-ahead for the Pearl Harbor attack.
On Dec. 6, 1941, the C-1s swam to points within 12 miles of Pearl Harbor. Then, between the hours of midnight and 3:30 A.M. the next day, the ships released their deadly payloads.