Source control was not a thing, but you could say that there was an ad hoc source control, resulting from all the administration around the project. Read further though, because there's more to Source Control than that.
The word did not exist, even the concept didn't exist. And there would have been no way to rollback the work instantly like you could do nowadays with git, but there was probably lots of traceability in the documents, so that nothing would get lost or forged.
Keep in mind that the development iterations back then were much much slower.
There were several reasons:
- Everything was handwritten or typed on paper, including schematics, etc.
- It was war time, so there was a lot of formal validation going on, like the officer to whom the team was reporting to had to sign documents constantly.
- Many peripheral tasks that were performed by specialized teams. There used to be rooms full of peope whose job was solely to perform complex calculations, fast. There were also people whose job was solely to punch cards.
All these documents had to go back and forth, and were constantly validated, and then archived. Formally, you may call that an embryo of source control, applied to a tiny team of like 10 people, tops. What I'm describing doesn't even accurately represent the daily work routine o Turing during WWII. What I'm describing is more of a 1960's NASA project.
"Modern", automated, dedicated source control is a billion lightyears away from that. If you're satisfied with such a lose definition of Source Control", then you could call anything source control. It wasn't even sources, only doodles and technical documents.
I would add that source control is not only meant to archive and rollback, but also to handle concurrent modifications. There were no such things in Turing's time, since his team and he were dispatching tasks after meetings gathering a handful of people.