Did the US have plans to use nerve gas in the invasion of Japan? I’ve never heard about that before.
The claim is made in an article by Paul Rogers, a professor of England's Bradford University, in his August 2005 article "By any means necessary: the United States and Japan" 1. The article references a story written by historians Norman Polmar and Thomas B Allen called "The Most Deadly Plan", which ran in Proceedings of the US Naval Institute in January 1998. The proposed nerve gas campaign is also described in Power At Sea: The Breaking Storm, 1919-1945 by Lisle A. Rose (2006, University of Missouri Press, ISBN-10: 0826217028), page 412 2.
Both of Rogers' sources refer to two U.S. Army Chemical Warfare Service studies: A Study of the Possible Use of Toxic Gas in Operation Olympic and Selected Aerial Objectives for Retaliatory Gas Attacks on Japan (April, 1944). According to Rogers
The main weapons to be used were two chemical blister agents, phosgene and mustard gas, together with hydrogen cyanide and cyanogen chloride.While I haven't read either the Army reports or the article from Proceedings, the claim sounds plausible to me.At the time of the invasion itself, tactical strike aircraft would drop nearly 9,000 tons of chemical weapons on the defending troops in the first fifteen days, with further attacks planned at the rate of just under 5,000 tons every thirty days from then on. As US troops came ashore, they would bring in howitzers and mortars that could deliver an additional forty-five tons a day of poisonous gas on Japanese positions.
This represented a massive use of chemical weapons, but it was dwarfed in scale by the proposed attacks on Japanese cities. In what the document described as an "initial gas blitz", long-range B-29 and B-24 strategic bombers would attack a large number of cities across Japan – starting with Tokyo, fifteen days before the ground invasion started. Over the next, initial fifteen-day period, over 56,000 tons of gas bombs would be dropped on cities, followed by almost 24,000 tons of gas bombs dropped every month from then on until the war ended or all the planned targets had been hit.
Although this plan was completed only in June 1945, it originated in work started by the Chemical Warfare Service more than eighteen months earlier; as early as April 1944, a detailed study – "Selected Aerial Objectives for Retaliatory Gas Attacks on Japan" – had been completed assessing the vulnerability of cities such as Tokyo, Nagoya and Osaka to gas attack. The analysts believed that their densely populated residential areas, with narrow streets and few open spaces, were particularly susceptible to chemical warfare. Moreover, mustard gas is readily absorbed by wood, and Japanese wooden houses would have been very difficult to decontaminate.
The intention was to maximise casualties, mostly civilian, and the study stated:
"The Gas Attack Program is aimed primarily at causing the maximum number of casualties, crippling transportation and public services, complicating and delaying the repair of HE [high explosive] bomb damage and making targets more vulnerable to incendiary attack."By June 1945, the full gas-attack plan was submitted to Major General William N Porter, head of the Chemical Warfare Service, detailing fifty urban and industrial targets, including twenty-five cities that were particularly susceptible to gas attack. According to the report, "Gas attacks of the size and intensity recommended on these 250 square miles of urban population … might easily kill 5,000,000 people and injure that many more." 3