Hi. Here is a photo of the prewar Polish Sokol 1000 motorcycle in military trim. It was used by, amongst others, the Reconnaissance Battalion of the 10th Cavalry Brigade (the Black Brigade). It was supposedly very reliable although outdated. My father rode one of these in the prewar Polish Army.
I suspect these would be nearly impossible to find and expensive to buy and run. What I'd like to know is which American bike of that era would closely match it? According to Wikipedia, the Polish Army used Harley Davidsons for a time and this design was based on the Harley with a copy of an Indian engine. Thanks.