In the last month, three of the four American SSGNs (former ballistic missile subs each now carrying 154 cruise missiles and SEAL commando teams) appeared in the Pacific and Indian oceans (the Philippines, South Korea and Diego Garcia). Some thought this was a message for China, but, in fact, the SSGNs go where the potential trouble is. When questioned, U.S. Navy officials responded that, for the first time, all four SSGNs were operating at sea, in locations distant from their bases.
Two years ago, the U.S. Navy completed the conversion of the last of four Ohio class ballistic missile submarines (SSBN), to cruise missile submarines (SSGN). Each of these boats now carries 154 Tomahawk cruise missiles, and provides space (for living, working and training) for 66 commandos (usually SEALs) and their equipment.
The idea of converting ballistic missile subs, that would have to be scrapped to fulfill disarmament agreements, has been bouncing around since the 1990s. After September 11, 2001, the idea got some traction. The navy submariners love this one, because they lost a lot of their reason for being, with the end of the Cold War. The United States had built a powerful nuclear submarine force during the Cold War, but with the rapid disappearance of the Soviet Navy in the 1990s, there was little reason to keep over a hundred U.S. nuclear subs in commission. These boats are expensive, costing over a billion each to build and over a million dollars a week to operate. The four Ohio class SSBN being converted each have at least twenty years of life left in them. The conversions weren't cheap, each one cost over $400 million.
The idea of a sub, armed with 154 highly accurate cruise missiles, and capable of rapidly traveling under water (ignoring weather, or observation) at a speed of over 1,200 kilometers a day, to a far off hot spot, had great appeal in the post-Cold War world. The ability to carry a large force of commandos as well was also appealing. The Ohio SSGNs can also carry a wide variety of electronic sensors and other data collecting gear. Thus in one sub you have your choice of hammer or scalpel, or just a tap on enemy communications. More capable cruise missiles are in the works as well. Whether or not this multi-billion dollar investment will pay off remains to be seen. But it's certainly a bold move, and the navy already knows that Tomahawks and SEALs work.
Like the SSBNs, the SSGNs will have two crews (each with 159 personnel, not including commandoes), which will switch places in the boat every 3-4 months, flying out (if need be) to wherever the boat is for the swap. The SSGNs will apparently spend most of their time on intelligence collecting missions. As such, it may be a while before you hear any details.
The three SSGNs recently sighted does make it clear that the U.S. Navy has shifted its main effort from the Atlantic to the Pacific. Between World War II and the end of the Cold War, the U.S. Navy concentrated on the Atlantic, where the Soviet Navy was expected to make its main effort. The Soviets never did, but the Chinese might.