The answer to your question:

from PB1605
is it possible for lawyers to write a handbook that is LESS THAN 300 pages???
is very surprisingly - an affirm.

But, IFF, the two principal authors are an Army LTC and a Marine LTC who "manage to co-operate, as they say" - and the publication is edited by a Navy CAPT ("adult supervision").

2010 Law of War Deskbook.pdf (DL from the CLAMO Publications page) - 248 pages:

Authors
LTC Jeff A. Bovarnick, JA, USA
LtCol J. Porter Harlow, USMC
....
Editor
CAPT Brian J. Bill, JAGC, USN
....
This Law of War Deskbook is intended to replace, in a single bound volume, similar individual outlines that had been distributed as part of the Judge Advocate Officer Graduate and Basic Courses and the Operational Law of War Course. Together with the Operational Law Handbook and Law of War Documentary Supplement, these three volumes represent the range of international and operational law subjects taught to military judge advocates.
Table of Contents

Introduction to Public International Law 1
History of the Law of War 5
Framework of the Law of War 17
Legal Basis for the Use of Force 25
GC I: Wounded and Sick in the Field 37
GC III: Prisoners of War 63
GC IV: Civilians on the Battlefield 91
GC IV: Occupation and Post-Conflict Governance 107
Means and Methods of Warfare 131
War Crimes and Command Responsibility 163
Human Rights 187
Comparative Law 201
Less than a 2MB download

Besides that particular reference, I also should have included the Library of Congress - Military Legal Resources (links to all kinds of original source docs, as well as CLAMO, etc.). The LoC page is worth saving as a favorite.

Now, excuse me while I get back to my lime green popsicle - how can you stand those purple grape things on your tonguee ?

Regards

Mike