Qualla: I-400: The Submarine That Carried Airplanes

I-400: The Submarine That Carried Airplanes: Introduction

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit AnonymousUnknown author, Public domain. Four trained men could prepare a floatplane for launch from a submarine in seven minutes. In 45 minutes, the crew could assemble, fuel, arm, and catapult all three aircraft from the deck. This was the operational tempo demanded by the I-400, an Imperial Japanese Navy submarine commissioned in 1944 that was less a conventional warship than a mobile airfield lurking beneath the Pacific. Carrying three Aichi M6A1 Seiran torpedo bombers inside a watertight cylindrical hangar mounted on her top deck, I-400 was built for a single audacious purpose: to sail undetected across the world's largest ocean and launch a surprise air strike against the Panama Canal. She carried enough fuel to circumnavigate the globe one and a half times. Until 1965, nothing bigger had ever submerged.

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Image: AnonymousUnknown author | Public domain

I-400: The Submarine That Carried Airplanes: A Figure Eight Beneath the Waves

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit Public domain. The I-400-class submarines were engineering marvels born of desperation. Their pressure hull had a unique figure-of-eight cross-section that provided the strength and stability to support the weight of an aircraft hangar on the top deck -- a cylindrical, watertight tube running a...

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Image: Public domain

I-400: The Submarine That Carried Airplanes: The Panama Canal Plan

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit AnonymousUnknown author, Public domain. The mission was straightforward in concept and staggering in ambition: Submarine Division 1 would sail four submarines -- I-13, I-14, I-400, and I-401 -- across the Pacific and launch ten floatplanes against the Gatun Locks of the Panama Canal. Six torpedoes and four bombs would ...

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I-400: The Submarine That Carried Airplanes: Operation Arashi and the Race Against Surrender

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit AnonymousUnknown author, Public domain. The new mission, Operation Arashi -- Mountain Storm -- called for I-400 and I-401 to launch six Seiran floatplanes in a nighttime attack on Allied ships at Ulithi under a full moon. Each pilot would receive a hormone injection to sharpen his night vision. The aircraft had their J...

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Image: AnonymousUnknown author | Public domain

I-400: The Submarine That Carried Airplanes: Black Flag and Three Torpedoes

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit AnonymousUnknown author, Public domain. On August 26, 1945, I-400 received orders to hoist a black flag of surrender and disarm. Her crew assembled all three Seiran aircraft and catapulted them unmanned into the sea, dumped their bombs, fired off every torpedo, and destroyed all logs, charts, and codebooks. The next da...

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Image: AnonymousUnknown author | Public domain

I-400: The Submarine That Carried Airplanes: Found at the Bottom

Tue, 17 Feb 2026 00:00:00 GMT

Photo credit AnonymousUnknown author, Public domain. For 67 years, I-400 lay undiscovered on the Pacific floor. On August 1, 2013, the Hawaii Undersea Research Laboratory's deep-diving submersible Pisces V located the wreck southwest of Oahu at great depth. The hull was completely intact, but the entire superstructure -- conning to...

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Image: AnonymousUnknown author | Public domain