On Sunday, November 16, 2014 4:04:40 PM UTC-7, Frank Whiteley wrote:
Have bothered to check on the A-14, but while I was looking at mask images I saw one with an A-14 dated 1944, so I suspect they were a WWII development, perhaps earlier.

Frank Whiteley

History of US WWII military oxygen systems he
http://goo.gl/teVK96