CANT Z . 511 The CANT Z . 511 was a four - engine long - range seaplane designed by Filippo Zappata of the " Cantieri Riuniti dell ' Adriatico " ( CRDA ) company . Originally designed for the Central and South Atlantic passenger routes , it was later adapted as a military transport and special raider . Design and development . The design for the construction of a large four - engine , twin - float seaplane began at the end of September 1937 , when the technical department of CRDA accepted the specifications of the LATI ( " Compagnia Ala Littoria " ) company , created in 1939 , who required a long - range seaplane for carrying mail , cargo and passengers to Latin America . These plans were cancelled on the outbreak of World War II , but a version of the aircraft was adapted for long - range maritime patrol , armed with 10 single - mount 12 . 7 mm ( . 5 in ) machine gun s in both sides , in two upper turrets , and belly positions . Plans were made to install 20 mm cannon s in a front turret or in a glazed nose position , and more machine guns in a tail position . For bombing , it was adapted to carry up to 4 , 000 kg ( 8 , 800 lb ) of bombs in an internal bomb bay and on outer wing positions : up to four launch racks , for 454 mm ( 17 . 7 in ) air - launched torpedo es for surface attack , or " " Maiale " " manned torpedoes or midget submarine s for special operations . The original engines were relatively underpowered , so Zappata asked the authorities for permission to acquire 1 , 193 kW ( 1 , 600 hp ) Wright Double Cyclone s from the United States . Due to the deteriorating international situation , however , he was unable to obtain authorization . The CANT Z . 511 civil aircraft could theoretically carry 16 passengers over 5 , 000 km ( 3 , 100 mi ) . Later , when adapted as a military transport , four 1 , 119 kW ( 1 , 500 hp ) Piaggio P . XII RC 35 were used , giving only adequate power to an aircraft weighing up to 34 tonnes ( 37 tons ) , giving it a maximum range of 4 , 500 km ( 2 , 800 mi ) . Flight tests . The Z . 511 had its first test flights at Monfalcone , Venezia Giulia ( north - eastern Italy ) between October 1940 and March 1942 . Between 28 February and 1 March 1942 , test pilot Mario Stoppani succeeded in taking off and landing fully loaded in very rough seas , with 1 . 5 m ( 5 ft ) waves and winds of 55 – 65 km / h ( 34 - 40 mph ) . The Z . 511 prototype was then transported to Grado , Venezia ( further away from the insecure Yugoslavian border ) for further evaluations ; the last test and operational flight occurred on 1 September 1943 , the same day that the Italian Armistice was signed . After the division of the Italian forces , one aircraft was appropriated by the Fascist " Aeronautica Nazionale Repubblicana " . However , it had been damaged only three weeks before by British fighters , which had strafed it on Lake Trasimeno where it was undergoing final trials . It was transferred to the seaplane base at Vigna di Valle . There it suffered from sabotage by base personnel to prevent it falling into the hands of either the Allies or the German s . The other aircraft , still under construction at the CRDA factory , was retained by Axis forces and scrapped for the metal , which was sent to Germany . Planned operations . In early 1942 , plans for a number of different long - range special missions were made . The unique and unusual ideas were proposed by the " Aviazione Ausiliaria per la Marina " ( Naval Aviation Service ) as well as strategists of the " Regia Aeronautica " . Several projects were considered :