Started by TomZ, March 19, 2022, 12:00:43 PM
QuoteThe Savoia-Marchetti SM-77 was the ultimate development of the twin hulled flying boat range designed and built by the major Italian aircraft company in the 20s and 30s. Just as the SM-66 was a three engined and larger version of the well known SM-55, so the SM-77 was a four engined and much larger version of the SM-66. The twinned hulls of all three types were essentially similar though, and with a similar cockpit arrangement mounted over the wing centre section. All three types used V-12 engines, some by Isotta Fraschini and some by Fiat, and most producing around 800 bhp per engine. In all cases the engines were mounted on struts above the centre section and in the case of the SM-55 and the SM-77, were paired so that the rear engines drove pusher propellers.The spans of the three types steadily increased from 78 ft for the SM-55, through the 108 ft of the SM-66, to the 117 ft of the SM-77, all the while maintaining a similar length of around 54 ft. While originally designed as civilian passenger transports, all three types were pressed into military service with the Regia Aeronautica as bombers or for maritime reconnaissance tasks, the SM-77 being the only one of the twin hulled types to see serious service during WWII. Although mostly operating in the central Mediterranean and the Adriatic, two of the big boats were sent down to the Red Sea to assist with Italian operation in Eritrea and Abyssinia, being based at the port of Masawa at the northern tip of Eritrea. Their tasking was mainly for reconnaissance and anti-shipping patrols in the Red Sea, but there was little traffic for the two boats and one was returned to Italy as there was more need for it around its home country.The remaining SM-77 carried on operating from Masawa, but little action was seen until the Allied offensive started in December 1940. Bomber attacks against Masawa, the prime port for the Italian forces, by 47 Sqdn Wellesleys commenced almost immediately and persuaded the RA that the SM-77 should attempt to return to Italy, flying across the Arabian peninsula, Palestine and the Med. In late January 1941 the SM-77 took off on its homeward bound flight and was almost immediately intercepted by RAF Gladiators operating from Port Sudan. As the SM-77 had no defensive armament at the time it suffered a large number of hits in the engines and wings, limiting its power and its range with serious punctures to its fuel tanks. The aircraft's captain, Tenente Ranallo, decided that the only way to save his crew was to surrender the aircraft and with white flags flying from both hulls, the SM-77 was escorted to Port Sudan.The wing and fuel tank damage was repaired enough at Port Sudan to get the aircraft as far as Egypt, whence it was flown by Ranallo and his co-pilot with an RAF security crew in the cockpit, and landed on the Nile near RAF Heliopolis, where it came under the care of the redoubtable Flt. Lt. Finlay Barker, Engineering Officer of 216 Sqdn. Barker later became famous for his conversion of time expired Wellesley bombers into the only long range PR force used by the Desert Air Force in the exceedingly long spanned shape of the Wellesley B(PR)III. Barker realised that the Italian aircraft was in very good condition apart from its recent combat damage and suggested to the AoC Middle East Air Force that they restore it to airworthy condition and use it in the anti-shipping role for which Savoia-Marchetti had intended it. As such capabilities were woefully lacking in the area at that time, approval was given, little knowing what was to be the result!Barker set about his task with enthusiasm, and finding that parts for captured Italian engines were totally unobtainable, decided to re-engine the aircraft completely. This resulted in the use of four Merlin IIIs, arranged back to back in dual strut mounted pods mounted above each hull. The rear engines were fitted with locally machined idler gears to reverse the direction of their propellers which were then re-installed facing forward. The SM-77 already had twin torpedo racks mounted under the centre section and these were adapted to carry British Mark XII weapons, and dispensed with the Italian manual fusing system, which involved a crew member leaning out of a hatch on the inner side of each hull and setting the fuses by hand, as the Mk XIIs could be fused electrically! Deciding that more versatility in the weapons load would be required, Barker arranged for sliding bomb racks to be installed in each hull, being traversed outward under the wings for an attack, each rack being able to carry up to four 250 or 500 lbs bombs or depth charges. When the racks loads had been expended they would be re-loaded once they'd been slid back inside the hulls.As the aircraft had no defensive armament whatsoever, a nose gun turret was fitted to each hull, giving the SM-77 considerable strafing power against ships or submarines, a capability sadly lacking in the 47 Sqdn Wellesleys being used up to then in the MR role in the Eastern Med. The turrets each held twin Browning 0.303 machine guns, later on increased to four guns per turret, matching the firepower of a Hurricane or Spitfire! Later in the aircraft's life it was fitted with an ASV radar dome under the starboard wing, with the plotting screen installed in the adjacent hull. This enabled any shipping to be spotted at much longer distances than previously and increased the number of kills considerably.Thus equipped the SM-77 was assigned to 47 Sqdn, being only MR tasked unit in the Eastern Med, and was found to be much better equipped than the Wellesleys for that task. Being such a distinctive shape, there being no Allied twin hulled flying boats, gave the SM-77 crews some advantage of surprise as Axis targets assumed it to be an Regia Aeronatica aircraft rather than being with the RAF. The SM-77 was clearly marked with RAF roundels and fin flashes, although somewhat crudely painted over the RA markings, but these were not visible in a head-on attack of course. The aircraft still maintained much of its RA colour scheme, although the centre section was re-painted with RAF colours being the area which had had most work carried out.The SM-77 flew against Axis shipping for a considerable time, and was quite successful, carrying a heavy weapons load and being able to defend itself quite well, at least in the forward sector. Targetting the Axis convoys and coastal patrols, the SM-77 sank a substantial tonnage of shipping, including two U-Boats. During its time with 47 Sqdn. a trials setup of twin 0.303s were fitted to hatches on the outer side of each hull, but these were less than successful as they shipped considerable amounts of water during take-off and landing and the experiment was short lived.It was intended that the SM-77 should be returned to the UK eventually, to be evaluated by the Marine Aircraft Experimental Establishment at Felixstowe, there being no other examples of the design held by the Allies, but it was not to be. Shortly after take-off from Port Said in late 1943 the SM-77 suffered an engine fire in its starboard forward Merlin, and this quickly spread to the aft engine of the pair. Despite valiant efforts by the crew to extinguish the fire, it burnt through the starboard pylon and the entire assembly detached from the airframe, damaging the starboard boom and tail surfaces en route. The aircraft became virtually uncontrollable, but the Captain managed to land reasonably safely, but breaking the port boom in the process. Because of the asymmetric weight loading the port hull started to sink until the sea came over the weapons loading hatch in the port boom and what remained of the aircraft rapidly turned turtle and sank, the crew managing to escape into the dinghies and rafts.Thus ended the short but active life of the RAF's only twin hulled flying boat, much loved by her English speaking crews and feared by her German and Italian speaking adversaries.
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