with the gun barrels positioned vertically, one aft of the other to reduce drag, giving the impression that the aircraft had additional antennae. Given the SM.81's cruise speed of around 270 km/h (170 mph) and the presence of a massive fixed undercarriage, the aerodynamic gain was relatively small. The ventral turret was operated in a different fashion to those fitted to other aircraft where the gunner occupied the ball- or dustbin-shaped structure; instead, due to lack of space, the gunner crouched in the fuselage with his head down inside the turret. This proved not to be very effective as were most ventral turrets, and they were not fitted to further Savoias, although Piaggio fitted a dustbin-style turret accommodating the gunner to their P.108. Both flanks were covered by one single and one twin gun installation. Initially six 7.7 mm (.303 in) Vickers machine guns were fitted, but these were later replaced by reliable, if not very fast-firing models made by Breda, together with 500 rounds per gun. The SM.81's bomb bay was divided into two parts with a passage linking aft and mid fuselage between, and could accommodate a wide range of ordnance up to a total of 2,000 kg (4,410 lb) over short ranges, with individual bombs of up to 500 kg (1,100 lb), arranged either horizontally or vertically: 4 × 500 kg (1,100 lb) (stored horizontally) 4 × 250 kg (550 lb) (ditto) 16 × 100 kg (220 lb) (stored vertically, as all the smaller ones), true weight around 130 kg (287 lb) 28 × 50 kg (110 lb) (true weight, around 70 kg/150 lb) 56 × 31 kg (68 lb), 24 kg (53 lb), 20 kg (40 lb), or 15 kg (33 lb) 1,008 × 2 kg (4 lb) (true weight, around 1,700 kg/3,750 lb) Incendiary bombs The bomb-release mechanism was located on the right side of the bombardier's position. The SM.81's defensive armament was better than its successor, the SM.79, and even than that of the SM.84, although of smaller calibre, but still insufficient when faced with modern enemy fighter opposition. It was also capable of carrying a greater bombload than the SM.79, due to its wide fuselage. Propulsion The SM.81 had a three-engine configuration, but unlike the Sparviero, was fitted with a wide range of engines throughout its production: Alfa Romeo 125 RC.35, 432–507 kW (580–680 hp). 192 built. Gnome-Rhône 14K, 485–746 kW (650-1,000 hp).96