After World War II, the French could not afford the most sophisticated military equipment, and so improvised with what they had on hand. Hence their production of scooter-mounted 75mm recoilless rifles. Blogger James R. Rummel offers more information and photographs of this vehicle.
http://www.hellinahandbasket.net/2009/04/that-is-a-really-loud-scooter.htm
That hurts...no, really, seriously painful.