Just wanted to share this book I read through recently. It is a discussion on "special operations" in the medieval context and I find that description fits what happens in my WFRP games pretty often. (Small group on a special mission). It has an overall discussion of how these things would work in medieval times and six specific missions reconstructed in detail. As a game master I found it to be a useful read that definitely gave me several ideas that I intend to implement in my games. Warhammer world being based on medieval Europe many aspects of the environment are easily transferable.
Hope it will be useful to you
(The $80 price tag that comes up is ridiculous, you can get it for something like $20 easy - just click around for options)