The SM.87was created by order of the Argentine branch of the airline Ala Littoria (Corporacion de Trasportes Aereas), which required a cargo-passenger seaplane for local flights. The chief engineer of SIAI, Alessandro Marchetti, decided to take the SM.75 transport aircraft as a basis, put it on floats and equipped it with the necessary equipment. The design did not undergo significant changes: the nose and middle of the fuselage were made of aluminum and were covered with sheets of light aircraft steel, the tail section was sheathed with plywood. The floats were also metal and were attached to the lower surface of the fuselage and wing with struts. The cockpit was spacious enough to accommodate the pilot, navigator, radio operator and mechanic technician. The inner cabin was designed for 20-24 passengers. The power plant of the seaplane consisted of three R&W SG3G "Twin Wasp" radial engines with a capacity of 1050 hp. with three-blade propellers. Taking into account the improvements made, the aircraft name was changed to SM.87.

By the time the working drawings were ready, Italy was in a state of preparation for the coming war and heavy transport aircraft were being transferred to the Air Force. The contract signed earlier provided for the supply of 5 seaplanes, but with the requirement to replace the American engines with the Italian Fiat A.80 RC.41 (1000 hp), since there were quite pertinent fears that by the beginning of construction the United States would impose a ban on their delivery. The contract was finalized in January 1940, and on August 18, representatives of the company reported that the construction of four SM.87s had been completed and that spare parts and assemblies were ready, which would be enough for five more aircraft. They were immediately assigned military numbers MM.447-MM.450, to which the registration codes I-INNO, I-IGOR, I-ILLA and I-IGEA were then added.

The seaplanes began to gradually enter service from September to October 1940, although there was a slight delay due to an accident on one of the SM.87s. The first two  were deployed on the Rome-Algeria-Barcelona line after the victory over France, and subsequently all SM.87s served the Rome-Cagliari-Rome and Rome-Cagliari-Pollensa-Baleari routes. During their active service, which lasted until 1943, they never met enemy aircraft. The first battle SM.87 (I-INNO) survived only in May, when, at the moment of splashdown in the Gulf of Albia, it was attacked by a heavy fighter "Beaufighter". The seaplane delivering 28 soldiers from Rome to Sardinia had little chance of surviving, but after several calls, the British fighter was only able to pierce the SM.87 fuselage with cannons and machine guns. killing three people on board. After a short renovation, it was re-commissioned. By September 1943, all four seaplanes were at air bases

The I-INNO plane was hijacked on October 1 by Italian pilots Francesco Martinelli and Falvio Gerardi, who flew to Brindisi to join the Allied forces. It was soon scrapped. The other three SM.87s were taken to Venice and taken over by the Germans. Here, their old registration codes were changed to D-AKBE , D-AJAB  and D-AJAJ for temporary storage. Options were discussed to transfer them to the aviation of the Italian Social Republic, but in fact they were used by the Luftwaffe command and their traces are lost by the beginning of 1945. The aircraft were probably transferred to Lake Constance in December 1943 and scrapped there.

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