In 1934, Italian aircraft manufacturer Savoia-Marchetti commenced work on what would become the SM.79. The design team was headed by aeronautical engineer Alessandro Marchetti. It had originally been conceived as a fast monoplane transport aircraft, capable of accommodating up to eight passengers and of being used in air racing (such as the London-Melbourne race). The design, which was initially designated as the SM.79P (P stood for passenger), was once intended to be a civil derivative of the Savoia-Marchetti SM.81, a militarised transport/bomber aircraft that was itself based upon the Savoia-Marchetti S.73 airliner.

The company quickly set about the construction of a single prototype of its design, being keen to participate in the high-profile London-Melbourne race if possible. According to aviation author Giorgio Apostolo, the SM.79 had adopted a three-engine configuration (two in mid-wing positions and the third mounted upon the nose) due to commercial safety concerns rather than for speed. Originally, there had been plans to adopt the 597 kW (801 hp) Isotta-Fraschini Asso XI Ri as the aircraft's powerplant; however, it was decided to revert to the less powerful 440 kW (590 hp) Piaggio Stella P.IX R.C.40, a derivative of the license-produced model of the British Bristol Jupiter, on which many of Piaggio's engines were based.

On 28 September 1934, the prototype SM.79 conducted its maiden flight, piloted by Adriano Bacula. Despite the company's ambitions to participate, the prototype (registration I-MAGO) had been completed too late for it to be entered in the London-Melbourne race. It featured very sleek contours and continuous panoramic windows, true to its original intended role as a passenger aircraft. Despite its delay, the prototype was able to quickly demonstrate its speed, conducting a flight from Milan to Rome in just one hour and 10 minutes, flying at an average speed of 410 km/h  On 20 July 1935, it was awarded its Certificate of Airworthiness. Soon after, on 2 August 1935, the prototype established a new speed record by flying from Rome to Massaua, in Italian Eritrea, in 12 flying hours (with a refuelling stop at Cairo, Egypt).

Various other world records were established during multiple test flights performed by the prototype. It was determined early on that it was the engines, rather than the airframe itself, that proved to be its limiting factor; accordingly, the prototype was re-engined multiple times. During 1935, the P.IX engines that had been originally installed were replaced by Alfa Romeo 125 RC.35s (this was a license-produced version of the Bristol Pegasus engine); during 1936, these were replaced by Alfa Romeo 126 RC.34s. The high performance demonstrated by the prototype attracted the attention of the Italian military, which approached Savoia-Marchetti with a request to investigate the prospects for producing a bomber-conversion of the type.

An evaluation of the SM.79 from a military perspective was conducted. Amongst the determinations made was that the installation of either two or three defensive machine guns would produce a highly effective defense against contemporary fighter aircraft. In response to the military interest, the company decided to construct a militarised second prototype.[7] While it did not differ in structure from the first civil-orientated prototype, it featured a faired ventral nacelle for a bomb-aimer, a forward-firing machine gun above the pilot's cabin, along with another machine gun located on the underside of the tail. Furthermore, a third machinegun could be installed at an open position aft of the dorsal fairing to provide for further rear defense.

During October 1936, production of the SM.79 formally commenced. Initially, focus was given to producing civil aircraft while military variants continued to be developed; as such, there were a pair of principal commercial variants produced as well, these being the speed-focused SM.79C (C standing for race) and the long-range SM.79T (T for Transatlantic). Aircraft amongst these variants participated in various early record-setting attempts during 1937 and 1938. In light of opinions amongst prospective export customers of the durability of a nose-mounted gun position (impossible due to the nose-mounted third engine), Savoia-Marchetti commenced work on the design of a two-engined model of the type, known as the SM.79B. This model, which featured a redesigned nose section that incorporated the bomb-aimer's position and an elevated position for the pilot, along with a single movable machine gun, performed its first flight during 1936.

In addition to the manufacturing activity performed by Savoia-Marchetti, in order to meet demand for the type, an Italian subcontractor in the form of Aeronautica Umbra, based in Foligno, also produced the type. Manufacturing of the type continued until June 1943, during which a total of 1,217 aircraft were completed, many of which were completed to bomber, torpedo-bomber, and transport configurations.Aviation author Bill Gunston described the SM.79 as being by far the most important Italian offensive warplane of the Second World War, and one of the very few Italian aircraft to be produced in substantial quantities.

The SM.79 was a cantilever low-wing monoplane trimotor, with a retractable taildragger undercarriage. The fuselage used a welded tubular steel frame structure, which was covered with duralumin on the forward section, a mixture of duralumin and plywood across the upper fuselage surface, and fabric for all of the other exterior surfaces. The wings were of all-wood construction, with trailing edge flaps and leading edge slats (Handley Page style) to offset their relatively small size. The internal structure was made of three spruce and plywood spars, linked with plywood ribs, with a skin of plywood. The wing had a dihedral of 2° 15'. The ailerons were capable of rotating through +13/-26°, and were used together with the flaps in low-speed flight and in takeoff. The aircraft's capabilities were significantly greater than its predecessor, the SM.75, with over 1,715 kW (2,300 hp) available and a high wing loading that gave it characteristics not dissimilar to a large fighter.

The engines fitted to the main bomber version were three 582 kW (780 hp) Alfa Romeo 126 RC.34 radials, equipped with variable-pitch, all-metal three-bladed propellers. Speeds attained were around 430 km/h  at 4,250 m , with a relatively low practical ceiling of 6,500 m . Cruise speed was 373 km/h  at 5,000 m , but the best cruise speed was 259 km/h  (60% power). The landing was characterized by a 200 km/h  final approach with the slats extended, slowing to 145 km/h  with extension of flaps, and finally the run over the field with only 200 m  needed to land (2,050 rpm, 644 Hg pressure).

The SM.79 was typically operated by a crew of five (or a crew of six upon the bomber version). The cockpit was designed for the accommodation of two pilots seated in a side-by-side configuration. Instrumentation in the central panel included oil and fuel gauges, altimeters for low (1,000 m) and high altitude (8,000 m) , clock, airspeed and vertical speed indicator, gyroscope, compass, artificial horizon, turn and bank indicator, rev counters and throttles.

The SM.79's performance was considered fairly strong. Its rate of climb was fairly high, it was fairly fast for its time, and was both rugged and responsive enough to allow it to be looped (with care). Its wooden structure was light enough to allow it to stay afloat for up to half an hour in case of water landing, giving the crew ample time to escape, and the front engine offered some protection from anti aircraft fire. With full power available and flaps set for takeoff, the SM.79 could be airborne within 300 m  before quickly climbing to an altitude of 1,000 m  within the space of 3 minutes, 2,000 m  in 6 minutes 30 seconds, 3,000 m  in 9 minutes 34 seconds, 4,000 m  in 13 minutes 2 seconds, and 5,000 m in 17 minutes 43 seconds.

The bomber version had 10 separate fuel tanks that had a maximum combined capacity of 3,460 L  Endurance when flown at full load was reportedly around 4 hours 30 minutes at an average speed of 360 km/h . The maximum ferry range, when flown at its optimal cruise speed, was unconfirmed; in order to reach Addis Ababa with non-stop flights from Libya, SM.79s were frequently modified in order to carry more fuel, and were able to fly over 2,000 km . The range (not endurance) with 1,000 kg  payload was around 800–900 km.

The effective torpedo bombing range was stated to be between 500 and 1,000 m  from the target. During combat operations, SM.79s would often fly at low level above hostile vessels prior to launching the aerial torpedo; as such, they were frequently targeted by every weapon available, from infantry small arms to heavy artillery, in a last ditch effort to prevent the torpedoes from being deployed. The Sparviero had several advantages compared to British torpedo bombers, including a higher top speed and greater range. Soon however, the Sparviero faced the Hawker Hurricane and the naval Fairey Fulmar, which was faster but still quite slow in relation to other escort fighters. Bristol Beaufighters were fast and well-armed, and as well as being effective long-range day fighters, were successful night interceptors and late in the war often chased Sparvieros in night missions. Curtiss P-40s, Lockheed P-38 Lightnings, Grumman Martlets and Supermarine Spitfires serving in the Mediterranean hindered Sparviero operations during the day.

The defensive armament of the SM.79 initially consisted of four, later increased to five, Breda-SAFAT machine guns. Three of these were 12.7 mm  guns, two of which were positioned in the dorsal "hump", with the forward one (with 300 rounds) fixed at an elevation of 15°, and the other manoeuvrable with 60° pivotal movement in the horizontal, and 0–70° in the vertical plane. The third 12.7 mm  machine gun was located ventrally. Each gun except for the forward one was equipped with 500 rounds. There was also a 7.7 mm  Lewis Gun in one of a pair of "waist" mounts, on a mount that allowed rapid change of side of the weapon. This Lewis gun was later replaced by two 7.7 mm  Bredas in the waist mounts, which were more reliable and faster firing (900 rounds/min instead of 500), even though there was only sufficient room in the fuselage for one man to operate them. Despite the low overall "hitting power", it was heavily armed by 1930s standards, the armament being more than a match for the fighter aircraft of the time, which were not usually fitted with any armour. By the Second World War, however, the Sparviero's vulnerability to newer fighters was significant, and it lost the reputation for near-invulnerability that it had gained over Spain.

No turrets were ever installed upon any SM.79s, which imposed considerable limitations upon its fields of defensive fire. Of all its defensive weapons, the dorsal one was often considered to be the most important as, following the shift to low-level attacks, the Sparviero was attacked almost exclusively from the rear and above. The defensive weapons located in the rear gondola and the rear hump were protected by aerodynamic shields, which were intended to only be opened in the event of attackers appearing. However, in practice, an enemy aircraft could attack the Sparviero while remaining unseen, so the defensive positions were usually left open even though this had the effect of reducing the aircraft's maximum effective speed.

The cramped layout of the ventral gondola, with the bomb-aiming instruments located in front and the rearwards-aimed ventral defensive machine gun in the rear, made it impossible to perform both bomb-aiming and rear defence simultaneously, so its usefulness was compromised. Because of this, in the later versions which were used exclusively for torpedo-bombing tasks, the ventral weapon and nacelle were removed. The fixed forward Breda machine gun, more suited to offensive tasks and aimed by the pilot, was seldom used defensively, and was often removed or replaced with a smaller calibre gun or mock-up, with an associated gain in speed and range due to the reduction in weight. The rear ventral gondola on the Sparviero was somewhat similar to the almost identically located Bola emplacement on the main wartime production -P and -H subtypes of the Heinkel He 111 German medium bomber, which was only used as a ventral defensive armament mount on the German aircraft.

As with the Luftwaffe's He 111, the Sparviero's bomb bay was configured to carry bombs vertically; this design decision had the consequence of preventing large bombs from being accommodated internally. The aircraft could accommodate a pair of 500 kg , five 250 kg , 12 100 or 50 kg  bombs, or hundreds of bomblets. The bombardier, who had an 85° forward field of view from their position, was normally provided with a "Jozza-2" aiming system, automatic cameras and a series of bomb-release mechanisms. The machine gun to the rear of the gondola prevented the bombardier from lying in a prone position, and as a result, the bombardier was provided with retractable structures to support his legs while seated.

From 1939 onwards, torpedoes were carried externally, as were larger bombs, with two hardpoints fitted under the inner wing. Theoretically, two torpedoes could be carried, but the performance and the manoeuvrability of the aircraft were so reduced that usually only one was carried. The SM.79's overall payload of 3,800 kg  precluded carrying 1,600–1,860 kg  of bombs without a noticeable reduction of the fuel load (approximately 2,400 kg , when full The standard torpedo, a 1938 Whitehead design, had a weight of 876 kg , length of 5.46 m  and a 170 kg  HE warhead. It had a 3 km  range at 74 km/h , and could be launched from a wide range of speeds and altitudes: 40–120 m  and up to 300 km/h  maximum. It took over ten years to develop effective torpedo-bombing techniques; consequently, with the failure of the SM.84 (its intended successor) and the lack of power of the Ca.314, only the SM.79 continued to serve as a torpedo bomber until 1944, despite trials conducted with many other types of aircraft, including the Fiat G.55S fighter.

• 
• 
• 

• 

• 
• 
•