Its mounted M20, a U.S.-made light anti-armour cannon, was very light when compared to a standard 75mm cannon but was still able to penetrate 100 mm of armour by so-called HEAT warhead. 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, enabling the weapon to be fired from the Vespa frame.
The scooters would be parachute-dropped in pairs, accompanied by a two-man team. The gun was carried on one scooter, while the ammunition was loaded on the other. Due to the lack of any kind of aiming devices the recoilless rifle was never designed to be fired from the scooter, the gun was mounted on a tripod which was also carried by the scooter, before being fired.
The "Bazooka Vespa" was relatively cheap: Vespas cost roughly $500 at the time, and the M20s were plentiful. Roughly 800 of these scooters were deployed in the Algerian War.
From: http://en.wikipedia.org/wiki/Vespa_150_TAP
