A twin-engined development of the SM.84 bomber, the SM.89 was an assault plane powered by 1350 h.p. Piaggio P.XII R.C.35 radial engines. Designed in 1941, it was under evaluation at the time of the Armistice. Forward-firing armament, mounted in the nose, consisted of two 37-mm. or 54-mm. cannon and two 12.7-mm. machine guns, while a defensive armament of two further 12.7-mm. weapons was fitted in dorsal and ventral positions. Loaded weight was 27,888 lb. Performance included a maximum speed of 286 m.p.h. at 17,388 ft. and a range of 683 miles. Dimensions were: span 69 ft. 03/8 in., length 53 ft. 92/3 in., and wing area 656.6 sq. ft. Piaggio P.XV R.C.35 radials of 1500 h.p. each were planned for later prototypes.