Agile System Engineering?

A friend and colleague of mine asked my a question: “Is there a good book on applying agile to system engineer?” I have to admit I did not know of any.  I have asked some of the deep experts I know and so far I have not received an answer. Perhaps one of you readers have a suggestion.

This question raises the issue what would agile system engineering be. My thought is that it could be “continuous engineering” in analogy with the DevOps  “continuous  delivery”  principle.  I have heard there is a “Continuous Delivery for Dummies” book in the works. It also could be applying lean principles to system engineering and development much in the spirit of lean software development. I think it is fair to say Agile is a flavor of lean.

Any and all comments, suggestions are welcome.