Justifications for punishment include retribution, deterrence, rehabilitation, and incapacitation. Sagan argued against nuclear proliferation, while Buckley promoted the concept of nuclear deterrence. Missile submarines played an especially important role in terms of strategic deterrence. Iran's military doctrine is based on deterrence. This marked the beginning of Pakistan's pursuit of nuclear deterrence capability. He specialized in nuclear deterrence issues. Agni V is primarily for enhancing India's nuclear deterrence against China. India is in the process of developing a nuclear doctrine based on "credible minimum deterrence". Prevention of future crimes (deterrence) or rehabilitation of the offender are other purposes of punishment. The financial costs attached to nuclear deterrence became an increasingly significant issue for the navy. This MAD scenario is often referred to as nuclear deterrence. The SDR considered this was the minimum number of warheads adequate for deterrence. These men were veterans of the cold-war who believed in using nuclear weapons for deterrence. Fisher was known for a unique idea towards nuclear deterrence. Afterwards paranoia grew and "preventive deterrence" spread.