Did Werner Heisenberg and Carl Friedrich von Weizsäcker compromise with the Nazis? The story begins with Albert Einstein, who became a target for conservative physicists like Philipp Lenard and Johannes Stark who could not follow Einstein’s physics, and the early Nazi Party that rejected Einstein as a Jew as well as his pacifism and internationalism. When Hitler came to power, Lenard and Stark gained great influence. Stark in particular tried to accumulate power but steadily lost influence through conflicts with other Nazis. When Stark’s nemesis, the theoretical physicist Arnold Sommerfeld, was going to retire and be succeeded by Werner Heisenberg, Stark launched a vicious attack on Heisenberg in the SS newspaper. Heisenberg appealed to SS Leader Heinrich Himmler and thanks to support from the aeronautical engineer Ludwig Prandtl was eventually rehabilitated by the SS. The established physics community then launched a counterattack against the “Aryan Physics” of Lenard and Stark, which included writing Einstein out of the history of relativity theory. This was arguably Heisenberg’s greatest compromise with Nazism.

Many historians have alleged – or strongly implied - that the days of late November/December 1941 witnessed an escalation of the Shoa from localised ethnic cleansing to genocide on a continental scale on account of the outbreak of US-German hostilities. According to this theory, Hitler managed to convince himself that the war was militarily lost by virtue of the Red Army’s winter offensive and/or the US entry into the war and hence, decided to prioritise the mass murder of his (perceived) domestic enemies. Antisemitism pure and simple is seen as the key driver. This theory is problematic to say the least, since the situation outside Moscow would not come to be regarded as critical before mid-December.

I have concluded that the decision for the Shoah had almost certainly been made by late November and that there is indeed evidence which points to this being influenced by the assessment of imminent US-German hostilities. Crucially, however, it was put on hold for about a fortnight when the Germans arrived at the mistaken impression that Japan would not join them in hostilities. Antisemitism may have been important but was still trumped by strategic calculation.