75 years ago, Japan and the US each developed chemical weapons and trained their troops to use them. Near the end of the Pacific War, the Imperial Japanese Army stockpiled vast amounts of poison gas for use as a last resort. The US military, meanwhile, drew up chemical weapons plans that would have devastated Japan. After the war, both the US and Japan concealed the truth concerning these weapons. But newly unearthed documents and personal accounts shed light on this dark legacy.