The standard strategic warhead yields 20 megatons, or 1666 times the power of Hiroshima's 12 kilotons.  Despite all the rhetoric about the "cold war" being over, Russian nuclear powered 941 Typhoon class ballistic missile submarines slip silently through our offshore waters like monstrous grey sharks, unseen, unheard and undetected.  Each ship carries two hundred nuclear warheads and the ballistic missiles to deliver them to our cities with pinpoint accuracy. An even deadlier submarine threat has been developed by Russia, the Severodvinsk, which out performs America's best. Russia spent an estimated $12.8 billion in 1997 for R&D in this area. Once in service, the main targets of this submarine's nuclear missile compliment will be American cities.  What would you actually experience if you were so unfortunate as to be near a 20 megaton nuclear explosion? First, there would be a thermal pulse producing blinding light for 20 seconds and a searing heat. If you were within a 23-mile radius of the explosion you would be burned to death and incinerated instantly. If you were closer than that, your body would be vaporized. Retinal burns would be produced up to 350 miles away. Five seconds later, a blast wave of 400-mile-per-hour winds, then a vertical updraft. A large mushroom cloud would rise, containing dust and smoke, and firestorms would begin. The day would darken to night as the atmosphere was obscured. A lethal fallout would occur 150 miles downwind, producing nausea and vomiting. Two weeks later there would be hair loss. Your bone marrow would be depressed and the platelets depressed, producing secondary hemorrhage from your mouth, nose, lungs and bladder, and bloody diarrhea.  During an actual nuclear attack, three-fourths of the United States would be burned up in 10 seconds. Sixty percent of the population would be dead with only 300,1-megaton bombs. It is assumed that with an all-out first strike on America, 10,000 megatons would be used initially and several 25 megaton bombs.  A 20 megaton nuclear bomb is the equivalent of igniting a solid block of TNT 900 feet square.