In 1941, Heinrich Himmler ordered the creation of a research station. The laboratory was based out of the Dachau concentration camp and was under the command of the Nazi SS's military wing, the Waffen-Schutzstaffel. Ostensibly, the lab was focused on studying diseases with the goal of protecting German troops. New documents reported by University of Tubingen ecologist Klaus Reinhardt, however, show that Nazi Germany was definitely also working on an offensive biological warfare program.
Under the 1925 Geneva protocol, Adolf Hitler was precluded from using chemical or biological weapons during the Second World War. But that didn't stop the Nazi Party from trying to weaponize diseases like malaria to use against Allied troops.
Though most of the research conducted at the Dachau lab was focused on defensive research—studying diseases and the insects that carry them—Reinahrdt also found evidence of research into a program to air-drop diseased mosquitoes with the aim of spreading illness. According to Reinhardt, “Hitler repeatedly and strictly ordered that biological weapons should not be used, even for defensive purposes... However, his order of ‘extreme’ efforts into defence from biological weapons left the door open for those authorities that attempted to circumvent Hitler’s biological weapons ban.”
Here's one example of how the Dachau entomological lab used this wiggle room:
In a progress report dated 23 September 1944 and marked ‘secret’, [lab head Eduard] May mentioned Anopheles research being carried out ‘in order to clarify the question whether an artiﬁcial mass infection of the malaria parasite on to humans is possible and how one can counter an action that aims at such mass infection. It is anticipated to extend these investigations also to other questions that fall under the area of biological warfare and that concern insects that inﬂict harm to humans’ (May’s emphasis). Unlike other authors, I ﬁnd these comments may be interpreted as defensive rather than offensive warfare. However, the protocols of the actual experimental trials provide a little more insight.
Reading through the details of the mosquito research, says Reinhardt, “This wording, particularly in the German original, strongly suggests that May knew about the planned work of mosquito release, he knew about the offensive nature of this research and he made a recommendation based on these trials.”
Reinhardt's research also suggested another research program, a classified project code-named Siebenschläfer, or Dormouse, that may have been intended to use fleas to spread the plague. Of course, much of the research would also have carried defensive goals, says Reinhardt: “perhaps its purpose was to prevent plague epidemics in the concentration camps that could bring SS guards into danger and, by increased mortality of prisoners, threaten the availability of work slaves that were already in short supply.”
The research is just another sign that, even after so many years, the full scale of the Nazi's campaign has still not fully come to light.