Japan’s Panama Canal Buster

Captain Ariizumi was disappointed that the Panama mission had been canceled and argued the decision with his superior officers. According to Captain Zenji Orita in his 1976 book I-Boat Captain, Ariizumi was told, “A man does not worry about a fire he sees on the horizon when other flames are licking at his kimono sleeve!”

Asamura recalled that he was not disappointed at the change in mission objective despite the intensive preparation because he knew the situation. “I understood the importance of the Panama mission, but the U.S. was on our doorstep and that was more imperative,” he said.

I-400 and I-401 received orders on June 25 for a two-part operation. The first phase was called Hikari (light). I-13 and I-14 were to offload four Nakajima C6N1 Saiun reconnaissance aircraft at Truk Island, where the planes would scout the American fleet at Ulithi and relay target information to I-400 and I-401. The second part of the operation, called Arashi (storm), involved the two I-400 subs launching their six Seirans to carry out kamikaze attacks on the U.S. carriers and troop transports in coordination with Kaiten (manned torpedoes).

Fake U.S. markings were applied to the Seirans on July 21, and two days later I-400 and I-401 set out following separate routes to reduce their chance of discovery. The mission, however, was plagued by problems. En route, a Japanese shore battery accidentally shelled I-401, and I-13, carrying two of the Nakajima surveillance planes, was sunk, most likely by an American destroyer. Additionally, I-400 failed to pick up a crucial radio message, which led to its missing its rendezvous with I-401. As a result, the attack was postponed until August 25, giving the two subs time to regroup.

I-401’s Commander Nambu recalled picking up Allied broadcasts on August 14 announcing that Japan would soon surrender, but he did not believe them at the time, assuming they were either propaganda or a trick. Even when Emperor Hirohito made his August 15 radio broadcast asking the Japanese people to “endure the unendurable,” the captain and lieutenant commander debated whether to continue the mission, return to Japan or scuttle the ship. Asamura said he missed the emperor’s surrender announcement because he was sleeping at the time, but was not surprised that Japan had to surrender as he knew the war was going badly.

Some of I-401’s crew wanted to go ahead with the plan to attack U.S. forces at Ulithi. In fact Nambu said that even after I-401 received specific instructions canceling the operation and ordering the sub back to Japan, some crew members wanted to keep the sub and become pirates instead.

Finally, I-401’s crew hoisted the black triangular surrender flag and on August 26 fired all of its torpedoes. The crew destroyed its codes, logs, charts, manuals and secret documents, and after punching holes in the Seirans’ floats, either pushed or catapulted them into the sea. I-400 surrendered on August 27 on its way back to Japan, and two days later I-401 encountered USS Segundo.

Captain Ariizumi appointed Lieutenant Bando, I-401’s chief navigator, to negotiate the surrender of his flagship to Segundo, in part because Bando spoke some English. Despite the Japanese navigator’s English training, however, Commander Johnson wrote in his war patrol report that he and Bando “held a doubtful conversation…in baby talk plus violent gestures.”

Johnson initially responded with disbelief to Bando’s assertion that I-401 carried 200 men, stating, “This could quite possibly be an error on his part, as I think the war interrupted English instruction.” But of course Bando’s figure was correct.

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