The Pratt Helmet Gun
“An invention of Albert Bacon Pratt in 1916 the Pratt helmet gun combined a helmet and a firearm all in one. The helmet gun was fired by blowing into a tube. While the helmet gun was never produced, Pratt was awarded a patent for his invention, patent # 1183492. It was a semi automatic firearm, with the recoil of the guns discharge blowing back the bolt and cocking the hammer. A strong spring drove the bolt back forward, supposedly fast enough that the user wouldn’t even feel or notice the recoil. ”