I recieved my copy of "History of the German Steel Helmet 1916-1945" today and I must say that it an excellent book!
The book is divided into these main sections:
First World War
Reichswehr & Freikorps
Military
SS (incl. Waffen-SS)
Paratroopers
Police
Civil Defense
Other organisations
Flight helmets
Non-German uses of German helmets
Helmet development during the Second World War
If you have any interest in the German steel helmets, I recommend you to buy this book!
/Marcus