4. The United States had plans to use chemical weapons if necessary
Neither the United States nor the Empire of Japan were signatories to the Geneva Protocol banning the use of chemical weapons, and the Japanese used poison gas in China earlier in the war. During the island-hopping campaign across the Pacific, the Japanese had changed their defensive tactics. Early in the war, the Japanese defended the beachheads, attempting to prevent US troops from establishing a position ashore. Later in the war, as the pre-invasion air and ship bombardments grew more deadly, the Japanese established positions inland, in caves and underground bunkers, where there was an element of protection from the bombardments.
Gas weapons were prepositioned in the Marianas, to be delivered to the troops after landing and to be dropped by B-29s prior to the invasion. Troops underground, unless they were in sealed bunkers with closed air systems, would be especially vulnerable to gas weapons, given the prevailing nature of the winds over the Japanese Islands. The United States planners also considered the use of chemical weapons against Japanese crops. A defoliant designated LN-8 was developed over the course of the war and was considered for use before the Japanese surrender rendered it unnecessary. Following the war, LN-8 was one of the chemicals which was developed into Agent Orange.