The Imperial Japanese Navy’s I-400 class were the largest submarines built in World War II, designed to travel 43,000 miles, surface off an enemy coast, and launch a hidden squadron of bombers. This episode follows Admiral Isoroku Yamamoto’s vision of 18 boats, the wartime cuts that left only three, and the engineering puzzle of mounting a 102-foot watertight hangar on a hull that had to survive deep-sea pressure.

You will hear how a figure-eight pressure hull and an offset conning tower solved one problem and created others, why the boat took 56 seconds to dive, and what life was like for 144 men without air conditioning, flush toilets, or enough bunks. The conversation covers the folding Aichi M6A Seiran floatplanes, luminescent paint for night assembly, the planned strikes on the Panama Canal and Ulithi Atoll, the biological weapons plan aimed at San Diego, the surrender to the USS Blue, and Operation Road’s End, which sank the boats to keep them from the Soviets.

• Why a submarine aircraft carrier needed a figure-eight hull and seven degrees of constant rudder
• How crews unfolded, fueled, and launched three bombers in 30 minutes in the dark
• The pontoon-free launch option and what it meant for the pilots
• Why pilots objected to repainting their planes with American insignia
• How the wrecks stayed hidden until the 2000s and the single Seiran that survives in a museum