Sources of Tactical Philosophy
The Art of War -- Sun Tzu
One of the best sources of tactical philosophy is The Art of War by Sun Tzu. Several translations of this important work have been published, each containing not only the text but also essays and commentaries on it by modern day scholars or by contemporaries of Sun Tzu himself. You should study these commentaries, as they will give you a great deal of background information and insight into the text.
The translation by Thomas Cleary is a good one to start with. Sunzi Speaks -- The Art of War translated by Brian Bruya has pictures to go along with the text -- a pretty painless way to see what Sun Tzu was talking about. Other translations by the Denma Group and Samuel B. Griffith are also excellent. The Denma Group even has a website about The Art of War -- www.victoryoverwar.com, which contains study questions for those of you who are really interested in the scholarly aspects of Sun Tzu's philosophy.
On War -- Carl Von Clausewitz
Von Clausewitz's 19th century style of writing sometimes makes this book slow going. It will give you some historical perspective on tactics, but Sun Tzu's book is more concise and efficient. I liked von Clausewitz's observation that "In War, everything is simple, but even the simplest things are difficult."
Warfighting -- General A.M. Gray, USMC
A concise masterpiece of tactical thought! Barely 100 pages long, this book explains in simple sentences how you need to prepare for war and fight war. Many concepts are directly applicable to police special ops.