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Vasco de Gama had several mission objectives including finding and joining the legendary Christian King Prester John and attacking Islamic force in the rear. This was more or less achieved by Vasco's son Cristovao whose 400 musketeers successfully fought alongside Ethiopian Forces against the Ottomans in 1541 as well as naval battles such as the Battle of Diu turning the Indian Ocean into a Portuguese racket.
So WI the Chinese Treasure Fleet of 1405 to 1435 was given objectives like these? Perhaps attacking the Timurid Empire from the Arabian Sea would keep them off China's land border?