Someone just walked off the street and sold me this helmet. It took me nearly 30 minutes of online research to identify the style as I do not get many helmets coming into my surplus store these days. I am not sure whether this is a version 1 (BPH-1) or a version 2. I was not able to find much info other than these were used by flight crews circa 1965. The placement of the microphone on the chin cup is pretty unusual. Any further information on this helmet would be appreciated.

Here is another view of the microphone.