Dhanur-veda, or military science, was taught by Dronacarya with all its confidential secrets of throwing and controlling by Vedic hymns. Gross military science is dependent on material weapons, but finer than that is the art of throwing the arrows saturated with Vedic hymns, which act more effectively than gross material weapons like machine guns or atomic bombs. The control is by Vedic mantras, or the transcendental science of sound. It is said in the Ramayana that Maharaja Dasaratha, the father of Lord Sri Rama, used to control arrows by sound only. He could pierce his target with his arrow by only hearing the sound, without seeing the object. So this is a finer military science than that of the gross material military weapons used nowadays. Arjuna was taught all this, and therefore Draupadi wished that Arjuna feel obliged to Acarya Drona for all these benefits. And in the absence of Dronacarya, his son was his representative. That was the opinion of the good lady Draupadi. It may be argued why Dronacarya, a rigid brahmana, should be a teacher in military science. But the reply is that a brahmana should become a teacher, regardless of what his department of knowledge is. A learned brahmana should become a teacher, a priest and a recipient of charity. A bona fide brahmana is authorized to accept such professions.