While not directly relevant to the CRUSADER period, this is a very good read by an expert on the subject. Highly recommended.

https://www.usnwc.edu/getattachment/1f40e9ba-42c9-4861-bc7e-c2554ec2909b/The-Other-Ultra–Signal-Intelligence-and-the-Battl.aspx

Here’s something (in Italian) about a Regia Marina wireless operator:

http://www.trentoincina.it/mostrapost.php?id=331

Happy reading!