The Killing Zone : A Professional's Guide To Preparing or Preventing Ambushes by Gary Stubblefield and Mark Monday. The best book I ever read on the subject and it applies to both Infantry and a lot is useful for Law Enforcement. Some of what is in the book I can vouch for from personal experience.

Also Bill Moore talked about lessons from Vietnam Vets I was exposed to a lot of that myself and it was a shame that the Army never did something to debrief and record those lessons.