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  • In August of 1945, as the world celebrates the end of the Second World War, out in the

    1945年8月 世界が大戦終結の歓喜に包まれる中

  • pacific the Americans make a puzzling discovery.

    アメリカ軍は太平洋上で 未知の存在に遭遇する

  • The US Navy has intercepted a Japanese submarine and it's unlike anything

    向かった先に 待ち構えていたのは

  • they've seen before.

    他に類を見ない 日本軍の潜水艦だった

  • Its scale is baffling.


  • But not only is it the world's largest submarine, it's an entirely new kind of weapon.

    全くの新兵器で 世界最大の潜水艦だった

  • A submarine that can launch torpedo dive bombers.

    雷撃可能な急降下爆撃機を 搭載していたのである

  • The American's have just stumbled across Japan's secret underwater aircraft carriers,

    この潜水空母とも呼べる 未知の存在に遭遇した米海軍は

  • and soon they'll uncover a sinister plan that could've changed the

    程なくして 戦局を左右し得たかも知れない

  • course of the war.

    不吉な計画の全貌を 知ることとなる

  • Japan's surprise attack on Pearl Harbor in December 1941 is an event that

    伊400型 潜水空母

  • galvanizes a nation.

    1941年12月 日本軍による 突然の真珠湾への攻撃は

  • Pulling a reluctant America into the Second World War.


  • The unprovoked and dastardly attack by Japan on Sunday...”

    傍観者だった彼らを 世界大戦へと引き込んだ

  • A day after the devastating attack, the United States declares war on Japan.

    "日本軍による 謂れのない卑劣な襲撃は–"

  • And the nation quickly mobilizes, firing up its enormous industrial might to crank out

    壊滅的被害を受けたその翌日 アメリカは日本へ宣戦布告する

  • ships, tanks and aircraft at a rate that'll soon bury Japan's military.

    即座に国を挙げて 船や戦車、航空機が大量に製造され

  • For the Americans, Pearl Harbor was a senseless and cowardly provocation.


  • But for the Japanese, the attack was something entirely different.

    アメリカは真珠湾攻撃を 無意味で卑怯な挑発と捉えたが

  • A calculated gamble and a long shot attempt at actually trying to avoid a full-scale war

    日本軍にとって重要な 意味を持っていた

  • with the United States.


  • Because as the Empire of Japan continued its ruthless conquest in Asia, the Japanese were

    アメリカとの全面戦争を 避けるべく打たれたものだった

  • convinced that it was only a matter of time before the U.S. intervened.

    当時日本はアジアの広域を 容赦なく支配していたが

  • And the architect behind the Pearl Harbor attack, Japanese Admiral Yamamoto was aiming

    アメリカがこれに介入するのは 時間の問題だった

  • to knock out much of the U.S Pacific fleet in one decisive blow.

    真珠湾攻撃の考案に関わった 山本五十六提督は

  • As a way to keep the United States out of the Pacific for at least another six months

    意表を突き米太平洋艦隊を 一網打尽にしようと画策する

  • and perhaps even forcing the Americans into negotiating a truce.

    少なくとも半年間 アメリカを太平洋から遠ざけ

  • But Imperial Japan grossly underestimated America's resolve.

    休戦交渉を有利に運ぼうと 目論んでいたが

  • And in the aftermath, Yamamoto knew America's military might would soon overwhelm Japan's.

    アメリカの取った行動は 大日本帝国の想定を覆した

  • Now faced with a war he cannot win, Yamamoto devises another strategy.

    そして山本長官は これが勝てない戦争であり

  • To make America reconsider a drawn out war in the Pacific, He'll bring the war directly

    やがて日本は圧倒されると読み 別の戦略を用意する

  • to America's Cities.

    アメリカ本土の都市へ 攻撃を行い恐怖を与えることで

  • But with the United States now on guard for Japanese forces, Yamamato will need a truly

    アメリカ国民の 反戦意識を高めようとした

  • stealthy weapon to reach the United States.

    だが当然のように アメリカ本土の警戒は堅く

  • A weapon the Americans would never suspect.


  • The concept of launching aircraft from a submarine originated before the Second World War.

    敵地への接近に気付かれる 余地のないものだ

  • But these earlier attempts were experimental trials usually involving a single lightweight

    潜水艦から航空機を飛ばす構想は 第二次大戦前からあったが

  • reconnaissance plane.

    早期のものは 小型で軽量の 偵察機を1機用いるだけの

  • What Yamamoto had in mind was far more ambitious.


  • A fleet of submarines that could carry multiple attack aircraft and strike fear into the enemy

    山本長官の考えはそれよりも 遥かに野心的だった

  • by launching surprise attacks on cities, only to submerge and disappear again

    複数の攻撃機を搭載し 奇襲攻撃により相手を恐怖に陥れ

  • In March of 1942, Japanese engineers were handed the enormous task of designing Yamamoto's

    たちまち潜水して 姿を消してしまう艦隊だ

  • secret weapon.

    1942年3月 技術者たちは 山本長官の極秘艦隊の開発という

  • To start, Yamamoto's aircraft carrying subs would need to be capable of launching full-size


  • torpedo dive-bombers.

    まず雷撃可能なフルサイズの 急降下爆撃機の

  • And engineers would have to design a catapult launching system.


  • And a mechanism to recover the aircraft and bring them back onboard.


  • But making the bombers fit inside a submarine would be an even bigger challenge.

    帰投後の機体を海上から 回収する能力も求められた

  • With a typical World War Two-era dive bomber having a wingspan of about 12 meters, engineers

    しかし攻撃機を再び船内に 戻すことは困難を極めた

  • would also need to design an entirely new dive bomber.

    当時の急降下爆撃機は 通常 翼幅が12メートルあり

  • One that could be folded up to fit inside the sub's hanger.

    技術者たちは機体の完全な 再設計を余儀なくされた

  • The submarines would also need to be able to reach any part of America's coastline,

    艦内の格納庫に 折りたたんで収納するためだ

  • thousands of kilometers away.

    また数千キロ離れた アメリカの海岸線へ

  • And then return all the way back to Japan without refueling or resupplying.

    どこへでも到達できる 航続距離が求められ

  • And it meant carrying nearly two million liters of diesel fuel and enough supplies to support

    無給油・無補給で 往復しなければならなかった

  • a crew out at sea for months.

    それは 200万リットルの燃料 数ヶ月分の食料と水を

  • Japan's secret underwater aircraft carriers would be designated as the I-400.


  • And they'd be enormous.

    日本海軍の秘密の水中空母は 伊400と命名された

  • Nearly twice the length of a typical German U-boat.

    船体は大型化し 全長はUボートの2倍に及んだ

  • To support the weight of the hanger and to keep the sub stable during carrier operations,

    格納庫の重量を支え 作業中の挙動を安定させるため

  • engineers innovated a double hull design.


  • Essentially two hulls stuck together.


  • It gave the mammoth I-400 nearly three times the displacement of even the largest

    まるでマンモスのような 伊400の排水量は

  • American submarine.


  • And the I-400 was still a formidable submarine in the conventional sense.

    また空母機能を抜きにしても 伊400の攻撃能力は驚異的で

  • Armed with eight forward mounted torpedo tubes and a massive deck gun.

    艦首に8門の魚雷発射管と 甲板に単装の14センチ砲を備え

  • And to fend off enemy aircraft, three triple-mounted anti-aircraft guns and a fourth single mounted

    艦橋には3連装の対空機銃3基と 単装の機関砲を搭載していた

  • gun on the sail.

    だが無論のこと 伊400の主力となる武器は

  • But of course the i400's primary weapons were its three torpedo dive bombers.


  • The element of surprise was an underwater aircraft carrier's greatest advantage.

    特筆すべきは 潜水空母の持つ 優れたアドバンテージだろう

  • And as the I-400 silently approached its target, its crew would already begin preparing the

    水面下で伊400が 密かに目標へ接近する間にも

  • aircraft.

    攻撃機は既に発艦準備に 取り掛かっていた

  • Mechanics would start by running heated oil through the aircraft's engines so they would

    整備士達は機体のエンジンへ 加熱したオイルを注入し

  • be warmed up and ready to launch.


  • The mammoth submarine would surface a few hundred kilometers from its target and the

    巨大潜水艦は目標の 数百キロ手前で浮上し

  • race would be on to get three bombers airborne.

    3機の攻撃機を射出するための レースが始まる

  • Each aircraft would be rolled out from the hangar onto the deck.

    機体が格納庫から 甲板へ搬出されるやいなや

  • Crews would then start the engine, unfold the wings and tail, lock floats into place,

    エンジンを始動し 主翼と尾翼を展開させ

  • and load armament.

    フロートを固定し 兵装を装填すると

  • One by one, the three aircraft would be launched using a compressed air catapult.

    圧縮空気式のカタパルトから 1機ずつ射出される

  • The whole process would take thirty minutes.


  • After which the I-400 would dive back to safety and silently wait for the bombers to return

    その後 伊400は再び潜航し 安全な水面下で

  • from their mission.

    攻撃機が帰還するのを 静かに待っていた

  • The torpedo dive bombers were cutting edge.

    雷撃可能な急降下爆撃機は 当時最先端で

  • They were designed specifically for the I-400 and could carry the largest bomb or torpedo


  • in Japan's naval arsenal.

    他の日本海軍機の中でも 最大の爆弾搭載量を誇った

  • Equipped with floats, the aircraft would land alongside the submarine to be hoisted back

    攻撃機はフロートを使い 船の真横に着水し

  • aboard using a collapsible hydraulic crane.

    折り畳み式のクレーンを用いて 船内へと収容された

  • The aircraft could also be launched without floats for greater range and performance,

    フロートを外した状態で 発艦することも可能だったが

  • but forcing pilots to ditch into the ocean after their mission.

    搭載量が増える変わりに 海上への不時着を余儀なくされた

  • The I-400 was a brilliant design, merging the stealth of a submarine with the offensive

    伊400は潜水艦の隠密性と 空母の攻撃能力を掛け合わせた

  • strike capability of an aircraft carrier.


  • But Japan's new super weapon would make no difference in the War.

    しかしこの日本の超兵器が 戦争の趨勢を変えることはなかった

  • On August 15, 1945, after nearly four years of brutal conflict and with American forces

    そして1945年8月15日 4年近くに及んだ悲惨な戦争は

  • closing in and the bombing of Japanese cities, Japan finally surrendered.

    主要都市への相次ぐ空襲の末 日本の降伏により終わりを告げる

  • The Americans first intercepted an I-400 off the coast of Japan two weeks after the surrender.

    終戦の2週間後 米軍は 日本の近海で伊400に初めて遭遇する

  • And at first they weren't exactly sure what it actually was.

    当初 彼らはその正体を 全く認知していなかった

  • The Japanese crew had thrown all of the attack aircraft overboard.

    乗組員達は攻撃機を 全て海中へ投棄したため

  • And at first the Americans believed the I-400 was designed to carry cargo.

    米兵達は伊400を 単なる輸送艦であると信じた

  • But they'd soon unravel the submarine's true purpose and why Japan never used them

    しかし潜水艦の真の目的と なぜ末期まで使用されなかったのか

  • in the War.


  • To start, many in Japan's Navy considered Yamamoto's underwater aircraft carriers

    日本海軍は 山本長官の水中空母構想を

  • to be a farce.


  • And the slow process of launching aircraft in the middle of a combat zone too dangerous

    戦場での浮上と 攻撃機の発艦作業が

  • for submarine crews.


  • But resistance to the concept would soon be the least of Yamamoto's concerns.

    しかしこれらの否定的な意見が 最たる理由ではなかった

  • Because it took nearly a year to design such an unconventional weapon.

    このような大掛かりな艦艇の建造には 1年以上の期間を要した

  • Construction of the first I-400s only began at the start of 1943.

    一番艦の建造は 1943年に始まったが

  • By then, the Japanese were already losing the War.

    既に日本の敗色は 濃くなる一方だった

  • After a crushing defeat in June of 1942, the Americans were pushing the Japanese back across

    1942年6月 日本軍の壊滅的な敗北の後

  • the pacific.

    米軍は日本を太平洋から 押し戻しつつあった

  • And Japan was running critically short on fuel and raw materials.

    日本軍は慢性的な 燃料不足と資材不足とに悩まされており

  • Delaying I-400 construction even further.

    伊400の建造は 予定よりも大幅に遅れていた

  • And Yamamato himself would never live to see any of his submarines completed.

    山本長官が伊400の完成を 見届けることは叶わず

  • In 1943, while on an inspection tour through the South Pacific, Yamamoto's plane was

    1943年 南太平洋における 戦地の視察中

  • downed by American forces.


  • What started as a plan to build a fleet of eighteen underwater aircraft carriers was

    当初18隻の建造が 計画されていた潜水空母は

  • eventually whittled down to just five.


  • And only three were ever completed.

    完成にこぎつけたのは 3隻にとどまり

  • The first entering service in 1945.

    運用開始は 1945年になってからだった

  • So late in the War that Japan's military had already all but collapsed.

    その頃には日本軍は ほとんど壊滅に追い込まれており

  • Launching sneak attacks on American cities with a handful of dive bombers would've

    僅かな攻撃機によって 米本土の都市へ爆撃を行うことは

  • been pointless.


  • Even a more strategic mission to bomb the Panama Canal was abandoned after Japanese

    パナマ運河攻撃という より戦略的な作戦も立案されたが

  • command felt that it too would've made little difference so late in the War.

    大戦後期においてその影響は 軽視され却下された

  • The only mission the I-400's would ever set out on was a last ditch effort to bomb


  • American forces as they amassed off a tiny pacific atoll.

    小さな岩礁に集結する米軍への 爆撃任務であった

  • But as the first I-400s traveled to their targets, Japan surrendered, finally ending

    しかし伊400が現地へ 到着した直後

  • the Second World War.

    日本は降伏し 太平洋戦争は終結する

  • Aircraft carrier submarines had always been a gamble.


  • A way to change odds so stacked against Japan, that only through sheer ingenuity could the

    戦争末期における絶望的な戦況を 変えることはできなかったが

  • tables be turned.

    戦局を左右しうる その独創的な存在は

  • And had the sub arrived at the start of the war it might've made a difference.

    登場が早ければ 歴史を変えていたかもしれない

  • But Japan's secret weapon wasn't without compromise.

    しかし問題が なかった訳ではない

  • The process of launching three aircraft was supposed to take 30 minutes.

    3機の攻撃機の発艦には 30分を想定していたが

  • But rarely could it be accomplished in less than 45.

    実際に45分を下回ることは 滅多になかった

  • A dangerous amount of time for such a large submarine to be surfaced.

    このような大型の潜水艦を 長時間浮上させることは非常に危険だった

  • And the I-400's bombers, while sophisticated in their design were rushed into service and

    搭載された攻撃機は 先進的な設計であったにも関わらず

  • built from lower grade materials due to shortages.

    資材不足により低質な 材料によって作らざるを得ず

  • They were notoriously unreliable.


  • Rarely could all three get airborne without some mechanical problem.

    3機全てが正常に 稼働するとは考えられなかった

  • And the enormous I-400's depth time, critical for getting out of danger, was nearly double

    また 安全な深度に達するために 伊400が必要とした時間は

  • that of American submarines.


  • Even submerged, it was still vulnerable.


  • With a hull that was riveted, not welded, it likely would have stood up poorly against

    船体は溶接ではなくリベットで 留められており

  • depth-charges.


  • Still, the Americans considered the I-400 to be a dangerous weapon.

    それでも依然としてアメリカが 伊400を危険視していたのは

  • Especially in the wrong hands.


  • And In 1946, with the Soviets demanding to inspect the subs for themselves, the American's

    1946年 ソ連軍が 伊400の引き渡しを求めたため

  • scuttled the I-400s off the coast of Hawaii and Japan.

    米軍はハワイと日本の沖合での 海沈処分を行った

  • Keeping their exact wreckage locations secret, and closing the chapter on an ambitious new

    米軍は沈没地点を秘匿し 野心的な超兵器の存在は幕を閉じた

  • kind of weapon, that in a different set of circumstances, might've changed the course

    この新兵器は時代を問わず 戦争の流れを変えたかもしれなかった

  • of the war.

    このビデオは Nebulaによって制作されました

  • This video originally appeared on Nebula.


  • A streaming site that I helped create.

    NeburaではMustardの動画を Youtubeでの公開前に視聴できます

  • Nebula is where you can watch Mustard videos before they're on YouTube.

    広告やスポンサーからの メッセージは表示されません

  • Without any annoying advertisements or sponsor messages.

    進行中のD-DayのReal Engineeringのシリーズ、 Wendover Productionsの長編ドキュメンタリー

  • It's also home to a growing number of Nebula Originals like Real Engineering's ongoing

    あなたのお気に入りのクリエイターによる 実験的なコンテンツも含め

  • series on the Logistics of D-Day, long-form documentaries by Wendover Productions, and

    Nebula Originalsの数は 増加しています

  • experimental content by your favorite creators.

    いま Curiosity Streamにサインアップすると Nebulaを無料で入手できます

  • Right now you get Nebula for free, when you sign up for CuriosityStream.

    Curiosity Streamを使えば 最高の映画制作者たちによる

  • With CuriosityStream you get to enjoy thousands of high quality documentaries by some of the

    高品質なドキュメンタリーを 楽しむことができます