The Savoia-Marchetti S.55 was one of the weirder flying boats to enter service
during the interwar period, but despite its strange looks it was actually very successful,
and it enjoyed a large production run – especially when compared to other flying boats at the
time - and frankly it looked really cool. It was first conceived in 1923,
when the Regia Marina, along with the newly formed Regia Aeronautica,
were looking to expand their capabilities. Part of this included the ability to project Italian
air power over the Mediterranean. Italy’s main rivals in this naval theatre, Britain and France,
both had sizeable fleets, and so the need arose for an amphibious aircraft capable of torpedo
bombing, conventional bombing, and minelaying. In response to this need, Savoia-Marchetti
submitted the highly original design that would become the SM.55. The design featured twin hulls
that were separated almost 15 feet apart, a thick three-section cantilever wing with the cockpit
located in the central leading edge, it would be powered by two engines arranged in a tandem
configuration above the wing, and the tail was supported by twin booms that connected to both
the wing and the twin hulls for added support. The twin hulls were made from wood, with the
frames in a mix of poplar, walnut, and ash, while the double planking was predominantly made from
cedar and plywood. Between these two layers of planks was a layer of cloth that was covered in
a special waterproof putty, all of this combined to make an extremely seaworthy structure:
both waterproof, and stable. The twin hull arrangement also removed the need for
balancing floats to be attached further out on the wings, which would help with streamlining.
The central section of the wing was by far the most important part of the airframe. Not only
because it connected the twin hulls, but it also housed the pilot’s cockpit, supported the huge
struts that held the twin engines in place, and it also carried the aircraft’s payload underneath.
As a result of this it was heavily reinforced, with several spars being made integral to the
upper structure of the hulls and extending throughout the entire span of the wing itself.
Designed to operate with a crew of five or more probably six, the S.55 normally had two pilots in
the central cockpit, a rear gunner in each of the twin hulls, and bomb aimer in the portside hull.
The hypothetical sixth crew member was an engineer who would maintain the engines during flight.
This is not mentioned in any of the sources I have found, except one which happens to be the
official aircraft manual that was issued by the ministry of aeronautics. However, the entire book
is in Italian, and while it does not specify a total number of crew members – as this was
an operating and maintenance manual – it does allude to a so-called engine driver’s station.
This, combined with the location of the engines would make sense.
As the engines were mounted above the wing, access to them was granted by a watertight hatch that was
located behind the cockpit, and so it makes sense that an engineer of sorts would be able
to service the engine during flight. Initially, the S.55 was designed to be powered by a pair
of Lorraine-Dietrich engines that produced 400hp each. The raised arrangement of these
engines was popular amongst designers of flying boats at the time, as it a) kept the equipment
as far away from seawater as possible, and b) completely reduced the risk of the propeller
kicking up or getting caught in said seawater. It did however mean that the two pilots now had
a spinning propeller above their heads at a proximity that would make modern health and
safety officials apply for emotional counselling, but as there are no records of decapitated pilots,
we can assume the system was safe enough. In terms of ordnance, the S.55 was designed
to carry all of its offensive payload under the central wing section – as
mentioned earlier. According to the official manual it could carry the following:
A single 800kg naval torpedo. A single 800kg high explosive bomb. It could also carry
two 500kg bombs. Four 250kg bombs. Or eight 104kg bombs. The release of the payload was
done electronically or mechanically by a control panel operated in the portside hull,
this also featured a modern, self-contained aiming system that could be operated by day
or night against moving or stationary targets. The prototype model of the S.55 was completed
at some point in early 1925, and after initial test flights it was sent for evaluation trials.
These trials included testing the aircraft at its empty and maximum loaded weights,
with a top speed recorded of 131mph in the air and a landing speed on the water of 56 mph. Its water
handling characteristics received universally high praise and its ruggedness and stability in
heavy seas vindicated the decision to go with the twin hull design. The only area in which the S.55
struggled was climbing. It wasn’t atrocious, but it wasn’t exceptional either, taking 16 minutes
to reach an altitude of 10,000ft and a full hour to reach its surface ceiling of 16,400ft.
In the following 12 months this problem was somewhat rectified with the installation of two
500hp Isotta-Fraschini V12s. The fuel load was also increased, which slightly reduced the top
speed for the benefit of a significantly greater range, and with these new performance figures the
Regia Aeronautica was ready to place the first of its production orders in 1925. However, the S.55s
fame would not come from its military career. Commercial variants of the S.55, known as the 55C
or 55P, were already being built and were operating on two different commercial routes
across the Mediterranean. However, in 1925 the original prototype set fourteen world
records for speed, altitude, payload, and most importantly: distance. This convinced
Savoia-Marchetti that their aircraft could be well suited for transatlantic flights,
and this would lead to the record-setting journeys that the S.55 is best known for.
In 1927 Francesco de Pinedo, an air force officer and a vocal advocate of the seaplane,
would embark as part of a three-man crew on what would be known as the “four continents” flight.
Starting on February the 13th, his S.55, dubbed the Santa Maria,
took off for the first leg of a journey that would eventually cover four continents and 29,000 miles.
Most of the journey was completed without incident, although unhappily the Santa Maria
was burnt to a crisp on an artificial lake in Airzona, courtesy of a carelessly discarded
cigarette. However, a replacement was sent by ship from Italy, and the Santa Maria II
flew across the eastern United States and Canada before returning to Italy.
Despite being an unarmed version of the military variant, the Santa Maria’s success
was a great boost for the possibilities of a transatlantic commercial service:
something that was of great value from both an economic and propaganda perspective to the
Italian Government. And as a result of this, further ambitious flights were attempted.
The improved S.55A would be the next to make headlines. This model featured 800hp
Isotta-Fraschini W-18 engines, a new top speed of 147mph, and an improved range of 1200-2100 miles
depending its configuration. Twelve of these new aircraft made a 6500 mile mass flight
from Rome to Rio de Janeiro in 1930, with the flight being led by Air Marshall Italo Balbo.
This flight would be overshadowed three years later by the North Atlantic crossing
of twenty-four planes for the occasion of the Chicago Worlds fair. For this
an aerodynamically-refined model, the S.55X, was used. Changes included much smoother hulls and
engine cowlings, fairings at the joining of all major components,
and new tree-blade all metal propellers. Although identical in weight to the S.55A,
the new model could now reach a top speed of 174mph with a range of 2794 miles.
One S.55X crashed at Amsterdam on the outward journey, and another at the Azores on the return
flight, but thanks to the provision of a backup, twenty-four S.55s made triumphant arrivals at
Chicago and New York. This flight, more than any other single accomplishment up to that point,
propelled Italy to a new level of prestige in the field of aviation during the 1930s.
Besides the more spectacular long-distance flights, the S.55 had a long career with the Regia
Marina, serving for more than ten years. Although 13 aircraft were listed as available in 1939,
the S.55 had by that time reached the end of its service life, and was withdrawn from service.
As a result, none of them would see any wartime service.
However, this isn’t quite the end of this aircraft’s story.
As a result of the S.55s early long-distance triumphs, development work began on a larger
model that was aimed directly at commercial travel rather than being a converted
military plane. This resulted in the S.66. The S.66 was generally similar to the S.55,
although it was considerably larger and was powered by three engines rather than two.
Much to the relief of the pilots, these were arranged in the pusher configuration
which kept the spinning propeller blades well clear of the still open cockpit.
Built as a fourteen-passenger commercial flying boat, the S.66 went into service in 1932
on the Rome-Caligiari-Trippoli route, as well as the one running from Rome to Alexandria. Later on,
thanks to the addition of more powerful 700hp engines, the passenger capacity was
increased to 18 and it had a top speed of 164mph. Not a great deal is known about the S.66, however
24 are known to have been built and they were operated as a civil transport from 1932 to 1939.
After this at least one was impressed by the Air Force for air-sea search and rescue operations,
but not much is known apart from that. Finding source material on these planes has been
especially difficult, and it looks like the just isn’t much on them in terms of records.
However, one example of the S.55 still exists today, which is nice as I think
it’s a rather good-looking plane despite its weirdness. It is located in Brazil,
indeed it was used for the first crossing of the South Atlantic by Brazilian pilots,
its fate has been shrouded in doubt as the TAM museum faced financial problems in 2016. However,
it looks like after a stint in temporary storage, it will be going to a brand new hangar in the near
future for the public to be able to see again. Savoia-Marchetti weren’t the only ones making
weird and wonderful flying boats in the interwar period, in fact there are some
truly adventurous examples out there that I plan to cover, but those are videos for another day.
As always, thank you all so much for watching, and I’ll catch you all next time. Goodbye.