aircraft. Since the engines were quite small, the fuselage did not blend well with the nose engine, even less so than the SM.79. Many windows were present to provide the fuselage interior with daylight, giving the impression that it was a passenger aircraft. The all-wooden wings had three spars to provide the necessary support, whereas the semi-elliptical tail surfaces were fabric-covered metal. The pilot and co-pilot were seated side-by-side in an enclosed cockpit, with separate cabins for the flight engineer and the radio-operator/gunner behind the cockpit. The bomb bay was behind the cockpit, together with a passage which linked the mid and aft fuselage, where there were three further defensive positions. The bombardier's position was located just below the cockpit, in a semi-retractable gondola, and differed from that of the SM.79, being both larger and in a location which was more favourable for communicating with the crew, and provided excellent visibility thanks to the glazed panel. Both this position and the cockpit had escape hatches, but for normal entry and exit there was a door in the left, mid-fuselage, and one in the aft fuselage. Equipment included an RA 350I radio-transmitter, AR5 radio-receiver, and a P63N radiocompass (not always fitted), while other systems comprised an electrical generator, fire extinguishing system, and an OMI 30 camera (in the gunner's nacelle). The aircraft, having a large wing and robust undercarriage, was reliable and pleasant to fly, and could operate from all types of terrain. It was surprisingly fast for its time and, given the power of its engines, especially compared to the similar Junkers Ju 52. It was better armed than the SM.79, but the increased drag combined with the same engine power reduced the maximum speed and cruise speeds as well as the range. No armour was fitted, except for the self-sealing fuel tanks. Armament The SM.81 was equipped with six machine guns providing a heavy defensive armament for a 1935 aircraft. Two powered retractable turrets, one dorsal (just behind the pilots' seats) and one ventral-aft, were each fitted with 7.7 mm (0.303 in) Breda-SAFAT machine guns, while single 7.7 mm (.303 in) Lewis Guns were mounted to fire through lateral hatches. The turrets were rotated by a "Riva-Calzoni" hydraulic system, while the guns' elevation was manual, and manual back-up mechanisms were provided for both the retracting and rotating systems. Once retracted, only the upper part of the turret was visible,