Herrman Reiner, Paul Pietsch Verlag, Stuttgart 2000

Love this to tears.  Has loads of great photos.  Is written in German. Detail of the attributes of the different helmets. This covers both officer and enlisted helmets in tabular format and is easy to understand. I choose this and the Laine above as my easiest sources.  However, this seems to fall short in Reserve forces. Seems very 'active component' oriented. No reference clearly explains the Landwehr / reserve set-up.  Oh there are descriptions of reserve crosses but how many units to the active?  Relative rarity of Reserve helmets. Double holes? What is really good here is the tabular way of showing the data.  I prefer the older Laine but objectively this is better, has better pictures and covers both enlisted and officer helmets. You cannot go wrong here great book some times hard to find. They show up on eBay every once in a while and are regularly quite cheap like $60.