The AMCA Troupes Aeról Portées Mle. 56 is a M20 75 mm recoilless rifle mounted on an Italian Vespa scooter used by the French Airborne Forces in Algeria and Indochina. Produced by ACMA, a licensed assembler of Vespas in France, it mounted an M20, a U.S.-made light anti-armor cannon which could be fired from the shoulder but still penetrate armour 100 mm thick. The recoil is counteracted by venting propellant gases out the rear of the weapon which eliminated the need for a mechanical recoil system or heavy mounts, which enabled the weapon to be fired within the Vespa frame. The weapon, ammo (attached to the side) and crew were dropped via parachute into action and the weapon could even be fired on the move.
I'm impressed. Any weaponry mounted on a BSA or Matchless of the period would have been subject to the frequent maintenance needs of the bike. A mean machine indeed. But the French ended by leaving both Indochina and Algeria.