The AL-12P was designed by A. Ambrosini and was a high-wing cantilever monoplane with a wood-ribbed fuselage covered with stressed molded plywood.[1] Its wing had a foliated spruce plywood spar and was covered with plywood although the ailerons were fabric covered.[1] It also had large slotted spoilers that could be opened perpendicular above and below the wing.[1] The pilot and co-pilot sat side by side in the nose which is made from plywood-covered welded steel tubes and was hinged to allow cargo to be loaded into the fuselage, a passenger door was fitted on the right hand side of the fuselage.[1] It could carry 12 fully equipped troops or the equivalent weight in equipment.[1] The company built 16 AL-12Ps for the Italian Army.[1]
After World War II, S.A.I.-Ambrosini modified at least one AL-12P to be powered by 2 × 225hp Alfa Romeo 115ter six-cylinder air-cooled engines and fitted with a revised undercarriage with shock absorber struts attached to the engine nacelles braced by V-struts from the fuselage sides.[2]