Flight Rome - Tokio in 1942

[Richard Aigner]

H. W. Neulen, in "Rommels italienische Flieger, Die Regia Aeronautica in Nordafrika 1940 - 1943", p.206, writes that a SM. 75 GA (for grande autonomia = long range) code I-BUBA, MM 60539 flew, in June/July 1942, from Guidonia via Saporoshje and Paotou (Mongolia) to Tokio. The plane returned, as it participated in a long range attack (ca. 3000km one way from Rhodes/Gadurra) on Port Sudan on May 23/24 1943.
What was the purpose of the flight? What was the freight?
TIA, Richard