Editing I-400-class submarine (section)

==Operational history==
As the war turned against the Japanese and their fleet no longer had free rein in the Pacific, the Commander-in-Chief of the [[Japanese Combined Fleet]], Admiral Isoroku Yamamoto, devised a daring plan to attack [[New York City|New York]], [[Washington D.C.]], and other large American cities.{{cn|date=June 2024}}

[[File:I400Crew.jpg|thumb|Officers of ''I-400'' in front of the plane hangar, photographed by the [[US Navy]] following the surrender of the submarine at sea, one week after the end of hostilities.]]

===Panama Canal strike===
Following an inspection of Rabaul in August 1943, Captain Chikao Yamamoto and Commander Yasuo Fujimori conceived the idea of using the ''sen toku'' (secret submarine attack) to destroy the locks of the [[Panama Canal]] in an attempt to cut American supply lines to the [[Pacific Ocean]] and hamper the transfer of U.S. ships. Intelligence gathering on the proposed target began later that year.<ref name=Sakaida36/>

The Japanese were well aware that American fortifications existed on both sides of the Canal. On the Atlantic, the large coastal artillery batteries of [[Fort Sherman]] had a range of 30,000 yards ({{convert|17|mi|km}}), preventing enemy ships from getting near enough to shell the locks. In the months following the attack on Pearl Harbor, air and sea patrols had been strengthened around both entrances, and [[barrage balloons]] and [[anti-submarine net]]s erected. In August 1942, the 88th Coast (Anti-Aircraft) Artillery unit was added to help defend against aerial attacks.<ref name=Sakaida36/>

As the war continued and Japan's fortunes declined, however, security around the Canal grew increasingly lax. In January 1944 Commander Fujimori personally interviewed an American [[Prisoner of war|prisoner-of-war]] who had done guard duty there. He told Fujimori that defensive air patrols had virtually ceased, since it was considered increasingly unlikely the Axis powers would ever attack the locks. This further convinced Fujimori of his plan's feasibility.<ref name=Sakaida44>Sakaida, p. 44.</ref>

A Japanese engineer who had worked on the Canal during its construction handed over hundreds of documents to the Naval General Staff, including blueprints of the Canal structures and construction methods. A team of three shipping engineers studied the documents and concluded that the locks at [[Miraflores (Panama)|Miraflores]] on the Pacific side were the most vulnerable to aerial bombing, but the [[Gatun Locks|Gatun locks]] on the Atlantic side offered a chance of causing greater damage, since it would be harder to halt any outflow of water. They estimated the Canal would be unusable for at least six months following a successful attack on the locks.<ref name=Sakaida44-45>Sakaida, p. 44–5.</ref>

To increase the size of the airborne attack force, Commander Fujimori requested that two additional fleet submarines still under construction at Kobe, ''I-13'' and ''I-14'', be modified to house two ''Seiran''s each, bringing the total number of planes available to ten.<ref name=Sakaida36/> It was originally planned that two of the ''Seiran''s would carry [[torpedo]]es and the other eight would carry {{convert|800|kg|lb|abbr=on}} bombs. They were to make a combined torpedo and glide-bombing attack against the Gatun Locks. Eventually though, torpedo-bombing was dispensed with, because only one ''Seiran'' pilot had mastered the technique.<ref name=Sakaida45-46>Sakaida, pp. 45–6.</ref>

The Panama Canal strike plan called for four aircraft-carrying submarines (''I-400'', ''I-401'', ''I-13'' and ''I-14'') to sail eastward across the Pacific to the Gulf of Panama, a journey expected to take two months. At a point {{convert|185|km|nmi|abbr=on}} off the coast of Ecuador, the submarines would launch their ''Seiran'' aircraft at 0300hrs on a moonlit night. The ''Seiran''s, without floats, would fly at an altitude of {{convert|4000|m|abbr=on}} across the northern coast of Colombia to the vicinity of Colón. Now on the Caribbean side of the isthmus, they would turn westward on a heading of 270 degrees, then angle south-west and make their final approach to the Canal locks at dawn. After completing their bombing runs, the ''Seiran''s were to return to a designated rendezvous point and ditch alongside the waiting submarines where the aircrews would be picked up.<ref name=Sakaida46-47>Sakaida, pp. 46–7.</ref>

Around April 1945, Captain Ariizumi, the man appointed to carry out the attack, decided the ''Seiran'' pilots would make ''kamikaze'' ramming attacks against the gates, rather than conventional bombing runs, a tactic becoming increasingly common as the war went against the Japanese.  The ''Seiran'' squadron leader had already suggested as much to Ariizumi earlier that month, though for a time this was kept secret from the other pilots. At the end of May, however, one pilot happened to observe a ''Seiran'' having its bomb-release mechanism removed and replaced with a fixed mount. Realizing the implications of this change, he angrily confronted the executive officer of the squadron, who explained that the decision to withhold this intention from the other men was made to "avoid mental pressures on the aircrews."<ref name=Sakaida46-49>Sakaida, pp. 46–9.</ref>

By 5 June 1945, all four aircraft-carrying submarines had arrived at Nanao Wan where a full-scale wooden model of the Gatun Locks gate had been built by the [[Maizuru]] Naval Arsenal, placed on a raft and towed into the bay. The following night, formal training commenced with the ''Seiran'' flight crews practising rapid assembly, catapult launch and recovery of their aircraft. There was also rudimentary formation flying. From 15 June the ''Seiran'' pilots made practice daylight bombing runs against the wooden gate mock-up. By 20 June, all training ended and the operation was set to proceed.<ref name=Sakaida49>Sakaida, p. 49.</ref>

===Ulithi atoll===
Before the attack could commence, [[Okinawa Prefecture|Okinawa]] fell, and word reached Japan that the Allies were preparing an assault on the Japanese home islands. The Japanese Naval General Staff concluded the Panama Canal attack would have little impact on the war's outcome, and more direct and immediate action was necessary to stem the American advance.

Fifteen American aircraft carriers had assembled at the [[Ulithi]] atoll, preparatory to making a series of raids against the home islands.<ref name=Sakaida49/> The Japanese mission was changed to an attack on the [[Ulithi]] base.

The attack on Ulithi Atoll was to take place in two phases. The first, codenamed ''Hikari'' (light), involved transporting four [[Nakajima C6N|C6N ''Saiun'' (Myrt)]] single-engined high-speed reconnaissance planes to Truk Island. They were to be disassembled, crated and loaded into the water-tight hangars of submarines ''I-13'' and ''I-14''. Upon reaching Truk, the ''Saiun''s would be unloaded, reassembled and then flown over Ulithi to confirm the presence of American carriers anchored there. Following the delivery, ''I-13'' and ''I-14'' were to sail for Hong Kong, where they would embark four ''Seiran'' attack planes. They would then head to Singapore and join ''I-400'' and ''I-401'' for further operations.<ref name= Sakaida51>Sakaida, p. 51.</ref>

The second phase of the Ulithi attack was codenamed ''Arashi'' (storm). ''I-400'' and ''I-401'' were to rendezvous at a predetermined point on the night of 14/15 August. On 17 August they would launch their six ''Seiran''s before daybreak on a ''kamikaze'' mission against the American carriers. The ''Seiran''s, each with an {{convert|800|kg|lb|abbr=on}} bomb bolted to its fuselage, were to fly less than {{convert|50|m|abbr=on}} above the water to avoid radar detection and the American fighters expected to be patrolling {{convert|4000|m|abbr=on}} above.<ref name=Sakaida52>Sakaida, p. 52.</ref>

Just before departing Maizuru Naval Station, the ''Seiran''s were completely over-painted in silver with American [[United States Air Force#History|stars and bars insignias]] covering the red [[Flag of Japan|Hinomarus]], a direct violation of the rules of war. This was an attempt to further confuse recognition if the aircraft were prematurely spotted, but it was not well received by the pilots. Some felt it was both unnecessary and a personal insult to fly under American markings, as well as dishonorable to the Imperial Navy.<ref name=Sakaida53>Sakaida, p. 53.</ref>

Following the attack on Ulithi, ''I-400'' and ''I-401'' would sail for Hong Kong. There they would take on six more ''Seiran''s and sail for Singapore, where fuel oil was more readily available. They would then join ''I-13'' and ''I-14'' and stage further attacks with a combined force of ten ''Seiran'' aircraft.<ref name=Sakaida51/>

On 22 June, ''I-13'' and ''I-14'' arrived at Maizuru Harbor to take on fuel. They reached Ominato on 4 July to pick up their ''Saiun'' reconnaissance aircraft. ''I-13'' departed for Truk on 11 July but never reached her destination. She was detected running on the surface, attacked, and damaged by radar-equipped [[Grumman TBF Avenger|TBM Avengers]] on 16 July. An American destroyer escort later arrived and sank her with depth charges.<ref name=Sakaida57>Sakaida, p. 57.</ref>

Japan surrendered before the Ulithi attack was launched, and on 22 August 1945, the crews of the submarines were ordered to destroy all their weapons. The torpedoes were fired without arming and the aircraft were launched without unfolding the wings and stabilizers. When ''I-400'' surrendered to the American destroyer, {{USS|Blue|DD-744|2}}, the U.S. crew was astounded at her size, nearly {{convert|24|ft|abbr=on}} [[Length overall|longer]] than the USS ''Blue'' and just as [[Beam (nautical)|wide]] &ndash; considerably longer and wider than the largest [[Tench-class submarine|American fleet submarine]] of the day.

===Operation Cherry Blossoms at Night===
{{Main|Operation Cherry Blossoms at Night}}
The Japanese conceived of an attack on the United States through the use of [[Biological warfare|biological weapons]] specifically directed at the civilian population in [[San Diego]], [[California]]. Dubbed "Operation Cherry Blossoms at Night", the plan was to launch aircraft from five ''I-400'' submarines near [[Southern California]] at night, who would then drop "infected flea" bombs on the intended target, in the hope that the resulting infection would spread to the entire Western seaboard and kill tens of thousands of people. The plan was scheduled for September 22, 1945, but [[Surrender of Japan|Japan surrendered]] on August 15, 1945, before the operation was carried out.<ref>{{cite web| url=https://www.npr.org/2011/04/25/135638924/where-to-find-the-worlds-most-wicked-bugs| author=Amy Stewart| title=Where To Find The World's Most 'Wicked Bugs' - Fleas| publisher=National Public Radio| date=April 25, 2011}}</ref><ref>{{cite web| url=http://www.japantimes.co.jp/opinion/2001/06/05/commentary/world-commentary/the-trial-of-unit-731/| author=Russell Working| title=The trial of Unit 731| publisher=The Japan Times| date=June 5, 2001}}</ref>