The papers, which are available for free at Paperless Archives
as well as the National Archives website,
is the work of British intelligence monitoring the German preparations for a full-scale invasion.
According to the intelligence reports, the Germans were planning on using chemical weapons in the invasion. Plans called for airplanes to be adapted to spray foot-and-mouth disease or mustard gas, as well as the use of shells laced with anthrax, which the reports indicated "result in 95% mortality, death occurring in 10-12 days."
The reports also indicate that the Nazis were planning on using gas on the British after convincing the German populace that the Brits were planning to do it first. According to the report:
"At the beginning of December a foreign diplomat indicated that the German authorities are fostering a belief in the intention of the British to use gas in their raids against Germany, and concludes that this propaganda is intended to prepare German public opinion for the German use of gas against the United Kingdom."
While the plans called for the gas to be used mainly on military targets, it did occur to the minds of those writing the report that the Germans may use the gas on civilians as well:
"While this might be worth while if, owing to lack of protective measures, the effect of morale would be serious, our knowledge of the Germans leads us to suppose that he will not disperse his air-borne gas effort on civilians generally. He may, however, use gas to cause panic among civilian refugees on the front of his advance with the object of blocking the roads in the track of our counter-attacks."
The reports indicated that preparations were already underway by the Germans, with "gas bombs distributed to German Aerodromes around the Frisian coast and in Western Germany, while another report mentions the unloading at Oslo of gas bombs sent by rail from Bergen."
The planned invasion, codenamed Operation Sea Lion, was postponed in September 1940 after the defeat of the Luftwaffe by the Royal Air Force in the Battle of Britain. German leader Adolf Hitler called off the invasion plans in January 1941.