From The Germans in Normandy, by Richard Hargreaves (Pen and Sword, 2006), Kindle Loc. 3557-59, 3575-95:
The purge of the Wehrmacht began immediately [the attempt to assassinate Hitler on 20 July]. On 22 July, centuries of tradition were brushed aside. The military salute was abolished, replaced by the deutsche Gruss – the Hitler salute – ‘as an outward token of gratitude for his miraculous escape’….
And then came the final act of surrender. On 29 July, Heinz Guderian abandoned centuries of impartiality at a stroke. The German Army would no longer remain aloof from politics. In future, the German Army would be Hitler’s Army. That day he ordered:
Every General Staff officer must be a National Socialist Leadership Officer, namely he must demonstrate that he is one of the ‘best of the best’ not merely in the realms of strategy and tactics, but also in the political realm through his exemplary attitude and active guidance and instruction of younger comrades in the Führer’s ideas.
I expect every General Staff officer to accept and convert to my views immediately – and to do so publicly. Anyone who cannot do so should ask to leave the General Staff.
The humiliation continued. Staff officers attending situation conferences before Hitler were forcibly searched to see if they were carrying weapons or explosives. Political commissars – National Socialist Leadership Officers – began appearing at front-line units in increasing numbers to imbue the German Army with the spirit of National Socialism. ‘If a commander failed to follow orders to fight to the last man, his political officer would report this to the Nazi Party,’ infantry officer Siegfried Knappe wrote. The Party, in turn, ‘would take action to have the commander relieved of his command’. On 1 August, Himmler introduced the Sippenhaftung – the arrest not merely of all the suspected conspirators, but their entire families, their homes, all their worldly possessions. ‘This man is a traitor, the blood is bad,’ the Reichsführer SS declared, ‘there is bad blood in them, that will be eradicated.’ The Stauffenberg family would be eliminated ‘to the last member’. Three days later, a specially convened ‘Court of Honour’ was set up to expel members of the Wehrmacht from military service so they could be tried in civilian courts for their involvement in the putsch. It was a formality. Each man was dismissed in ‘only a few minutes’. Gerd von Rundstedt was wheeled out of retirement to preside over affairs. The elderly field marshal had his doubts, but passed judgment anyway. The leading conspirators, including Hoepner and Witzleben, were led before the People’s Court set up to try them on 7 August. The verdict was swiftly delivered: guilty; the penalty, death by hanging the following day at Plötzensee prison in Berlin’s north-western suburbs.
The Luftwaffe and Kriegsmarine fared no better as a National Socialist broom swept through all three branches of the Wehrmacht in the aftermath of 20 July.