Annie Jacobsen has written this book about DARPA that is really enjoyable to read. I’m not all the way through with it, and though the title might (has) lead some to think it’s about conspiracy theories, it’s actually not. Jacobsen interviewed a lot of people who have worked there and it is a history.
If you’re uncertain if you’d like this book, you could try a sample, the first chapter, which discusses what happened when they tested out the Castle Bravo bomb.* It completely hooked me.
I’ve only read the first part of the book, but it goes into the arms race and how DARPA (and ARPA as it was once called) came to be. It also goes into some of computing history and obviously military history. There is already a lot that you could use in a science fiction book easily.
You might also try this Author Debriefing podcast from Spycast, where she discusses the book, and does an amazing job selling it herself. I had not even finished the podcast before I’d purchased the book.
*Castle Bravo hydrogen bomb test is one of the things that helped to inspire Godzilla, hence the use of him.