Elephants in Ancient Indian Warfare: https://www.worldhistory.org/article/1241/elephants-in-ancie...
Ancient Indian Books on Elephants: https://www.wisdomlib.org/hinduism/essay/elephantology-and-i...
Gajasastram — an ancient elephant treatise of India: https://nanjappavikram.medium.com/gajasastram-an-ancient-ele...
See also The Elephant Lore of the Hindus (Matangalila of Nilakantha) translated by Franklin Edgerton - https://en.wikipedia.org/wiki/Matanga_Lila