The first SIOP was developed in 1962, and stayed pretty stable throughout the Cold War. That was a time when you knew who your key strategic enemies were. But things changed in the 1990s. The Cold War ended, and the age of terrorism began.
SIOP details have always been kept secret, lest the enemy, or the American tax payer, discover how many nuclear weapons were aimed at what targets. This would tell potential enemies how good, or not-so-good, American intelligence was on those targets. This was particularly true during the Cold War, when Russia and China had many secret underground headquarters and weapons storage areas. The U.S. currently has about 8,000 active (ready for use) warheads, and some 2,500 in reserve. Russia and China still have many, probably over three thousand, nuclear warheads aimed at them. But many more are now aimed at nations like Iran and North Korea, that do not have reliable ICBMs aimed at the United States. What these two nations do have is the capability to provide terrorists with nuclear weapons, and thats what makes Iran and North Korea targets for American nukes. This much of the SIOP has been revealed in the last few years, as a reminder that, if Islamic terrorists get their hands on nukes, the suppliers can expect nuclear retribution if any of those nukes are used.
What are Americas options when it comes to nuclear weapons? They exist, and are all laid out in the SIOP (Single Integrated Operational Plan). This is a top secret document, and has been undergoing a lot of revision since the end of the Cold War in 1991, and the beginning of the war on terror a decade later. The current version, officially called OPLAN (Operation Plan) 8044, was adopted in late 2004. This one apparently has nuclear missiles aimed at Iran and North Korea, and perhaps other Middle Eastern nations as well. Just in case theres a nuclear terrorist attack, and the American people demand retribution.
Another big change since the end of the Cold War has been the speed with which ICBMs can have their targets changed. This is the result of improvements in hardware and software.
Would an American president actually give the order to retaliate using nukes? No one will know for sure until the unthinkable happens. Meanwhile, why are 10,000 warheads still in service? Mostly out of habit. Theres a substantial bureaucracy, and much inertia, working against attempts to reduce the size of the arsenal Even the nuclear arsenal is considered pork, because it costs billions of dollars a year to maintain all those warheads. The arsenal could probably be reduced by 90 percent, but no one is expecting that to happen any time soon.