Persian elephants, despite a recent assertion to the contrary, are unlikely to have carried turrets at Gaugamela (331 BC). Their active participation in the battle is also doubtful. Problematic sources such as the Fragmentum Sabbaiticum and the Itinerarium Alexandri should not be used unqualified to supplement the more well-recognized accounts of the engagement.
Charles, MB 2009, 'Turrets, Gaugamela and the historian’s duty of care', Scholia, vol. 18, pp. 29-36.