There is hardly a piece of hardware more iconic of the Cold War than the nuclear-powered submarine. Both nuclear-powered, and, in some cases, nuclear missile-equipped, these submarines have circled the world's oceans since the launch of the first nuclear submarine, the USS Nautilus, in 1954. Today, five nations (United States, Russia, France, the United Kingdom, and China) operate hundreds of nuclear submarines around the world. For all these countries, missile-launching submarines form an important part of the nuclear triad, which includes land-based missiles, strategic bombers, and ballistic missile submarines (SSBNs).
A nuclear submarine has a huge advantage over what it replaced -- the diesel-powered submarines. Large, military diesel-powered submarines, which had been built since the Revolutionary War, required air for combustion to generate electricity for batteries. Diving times were limited to a few days at slow speed, or just a few hours at top speed. The need to resurface put submarines are great risk of attack. In contrast, nuclear-powered submarines are self-powered, and their dive times are generally only limited by the available food supply and the sanity of the crew. A modern nuclear submarine can operate for their entire 20 or 40-year lifetimes without refueling.
Nuclear submarines tend to be extremely expensive, as costly as the most expensive and sophisticated aerial bombers. The Virginia class submarine, a series currently being constructed for the United States Navy, costs about $1.8 billion USD (US Dollars) per unit, in part due to a lack of economies of scale and high requirements for safety and reliability. The hull of submarines must be crafted in a very precise manner for the submarine to be able to sustain the greatest possible hull pressures during deep dives. Modern nuclear submarines have a test depth (maximum depth allowed during peacetime operations) of about 1,600 feet (488 m), at which point the pressure is about 48 times as great as at the surface.
The nuclear submarines, operated only by the world's nuclear powers, are generally split into two classes: the attack nuclear submarine and ballistic missile nuclear submarine. Attack submarines, such as the Seawolf, Los Angeles, and Virginia class, are armed with dozens of torpedoes and cruise missiles, which can strike targets hundreds of miles away. Ballistic missile submarines, such as the Ohio class, each carry 24 nuclear-tipped Trident ballistic missiles.