Gordon Williamson 
World War II German Police Units [PDF ebook] 

The German Police were an essential arm of the Nazi regime; as soon as Hitler achieved power the previous decentralized provincial system was unified into a single state apparatus, integrated at the command levels with the SS. While it may have been centrally controlled, it was still separated into a bewildering range of different departments and functions, many with their own uniform distinctions. This book offers a concise introduction to the organization, responsibilities, uniforms and insignia of the various branches of this machinery of repression, from Police generals to rural constables, transport policemen and factory watchmen.