They have discovered this atomic weapon–they require so many chemicals. But when you come to the higher stage, subtle, then mantra and water will do. Nothing more. No more chemicals. Simply mantra and water. That is yet you have to learn. But these things are there in the Vedas. If you are a serious student of Veda you can also learn, you can also fight like Arjuna. There is no difficulty. Therefore Krsna says astra-jnah. Unnaddham astra-jnah. You can also become learned in the higher science of military art. You can also utilize. But that requires brain, good brain.
Prabhupada Lecture Srimad-Bhagavatam 1.7.28-29 Vrndavana, September 25, 1976