Hi! I would recommend the reprint of "Handbook of the German Army 1918" by Battery Press (1996). Originally (re-)issued by the British General Stuff in different editions until April 1918, they represent the results of the intelligence service on the enemy army and deal with many aspects of it like equipment, recruitment, services, weaponry. In that way maybe sometimes slightly inaccurate but a wealth of information and in fact a prime source of many books of anglophone authors.
Beside this diverse Osprey books are also a nice read with entertaining pictures.
They shall grow not old,as we that are left grow old: Age shall not weary them,nor the years condemn. At the going down of the sun and in the morning. We will remember them.
I've always found Stephen Bull's World War One German Army very useful.
Part of Brassey's History of Uniforms series.
Downloadable here and Abebooks seem to have some at about £12. Plenty of copies on t'Internet.
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"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.
Imperial German Army 1914-18 By Herman Cron Gives info on just about everything from the Kaiser all the way down to Paul Baumer. by jus t about, it means there is no explanation of Veterinary services. for along time one of the only good references available in English for a long time.
Greetings Josh
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"General, you have nobly protected your forts. Keep your sword...to have crossed swords with you has been an honor, sir." General der Infantrie, Otto von Emmich