In 1538 there was a sea battle between the Ottomans and the Portuguese near the Indian port of Diu.  Notable success remained elusive and, from the 1540’s onwards, expansion towards the Indian Ocean was pursued with rather less vigor.  Nevertheless, the rulers of the principality of Atjeh in northern Sumatra, who wanted the sultan’s help in their own fight against the Portuguese, were granted military support in the form of cannons and gunners.  Independently of such ‘military missions’, Ottoman firearms specialists also seem to have found their way to the Indian subcontinent.  Moreover, the Ottoman sultans made occasional pious donations to mosques on the west coast of India, for instance in the town of Calicut. Since most of the merchants active in the Indian Ocean at  that time were already Muslims, such donations may have been inspired partly by the desire to create a political basis for the Ottoman sultans among these people.  In the end, however, it was not the Ottomans, but rather the Mughal rulers of Delhi and Agra who brought the trade center of western India under their control.

On both sides, the conflict between the Ottomans and the Portugese, who had themselves experienced economic and political difficulties in the second half of the sixteenth century, was seen as a religious matter.  The Portugese saw themselves as the patrons of Catholic missions, and their settlement in the Indian port of Goa was soon used as the base for missionary activities in the Far East.  During their expansion in southern Asia, the Portuguese kings and their officials always saw Muslim rulers and traders as their main enemies.  Meanwhile, the Ottoman sultans, in their capacity as protectors of Islam, were approached by the rulers of Atjeh for support.  Ottoman rulers also saw ‘religion and state’ (the formula used in many official documents) as indivisable.

ref: Faroqhi, S (2007). Subjects of the Sultan (pg 38-39) London: I.B Tauris & Co Ltd.