Prabhupada used the weapons of the materialists against them.

"One should not give up anything which can be utilized in the service of the Lord. That is a secret of devotional service. Anything that can be utilized in advancing Krishna consciousness and devotional service should be accepted. For instance, we are using many machines for the advancement of our present Krishna consciousness movement, machines like typewriters, dictaphones, tape recorders, microphones and airplanes. Sometimes people ask us, 'Why are you utilizing material products if you condemn the advancement of material civilization?' But actually we do not condemn. We simply ask people to do whatever they are doing in Krishna consciousness. This is the same principle on which, in the Bhagavad-gita, Krishna advised Arjuna to utilize his fighting abilities in devotional service. Similarly, we are utilizing these machines for Krishna’s service. With such sentiment for Krishna, or Krishna consciousness, we can accept everything. If the typewriter can be utilized for advancing our Krishna consciousness movement, we must accept it. Similarly, the dictaphone or any other machine must be used. Our vision is that Krishna is everything. Krishna is the cause and effect, and nothing belongs to us. Krishna’s things must be used in the service of Krishna. That is our vision."

 

(Nectar of Devotion, Chapter 14)