Sentence:  Since the magnitude of the plan made secrecy impossible , <WSD>once</WSD> the wheels had began to turn , persons controlling German industries , social institutions , and armed forces became , through their anti-Semitism or their tolerance of it , conscious accomplices of Hitler 's crimes ; whether in the last degree or a lesser one was a matter to be determined individually . 
Meaning of the word marked with <WSD> tags:  as soon as