Japan's recent tiptoeing around constitutional language that prohibits "cooperative self-defense" as it relates to joint missile defense efforts with the United States is only the latest in a decade-old process of redefining the Japanese Self-Defense Force (JSDF). In 1996, Japan's Embassy in Peru was attacked by the Shining Path rebel group and Japanese nationals were taken hostage. Japan was suddenly confronted with the fact that it had neither the capability nor the legal authority — even at home — to respond militarily. Thus began a profound rethinking in government, military and security circles of what Japan really needed out of its armed forces. The conclusion was: much more. Since then, Japan has slowly expanded its defense budget, spending nearly $45 billion in 2005. North Korea's July 5 missile tests provided a renewed justification for the substantial financial commitments required for missile defense. Several of the short- and medium-range missiles that North Korea tested were capable of striking Japan. Although the shorter-range missile tests received little international attention, they demonstrated a robust, direct threat to Japan (which is also concerned about China's ballistic missile capabilities). Japan is in a unique position for ballistic missile defense (BMD). The Cold War controversy that culminated in the 1972 anti-ballistic missile (ABM) treaty, which heavily restricted BMD capability, centered around the destabilizing effect an effective missile defense shield would have on the delicate balance of mutually assured destruction. Because Japan is wealthy, it can afford an investment few nations can. But because Japan is also not a nuclear power — in reality, because it is not the United States or Russia — its missile shield does not raise the same issues in terms of the world's nuclear balance. China, however, will not be pleased. The JSDF hopes to spend nearly $120 million to purchase and field the U.S. Patriot PAC-3 system, which provides a terminal phase defense, although the maximum altitude for a Patriot PAC-3 intercept is less than 10 miles. In terms of BMD, the Patriot PAC-3 provides a solid final line of defense, but it is only one component of a larger, layered defense with several interceptors of different capabilities. Alone, the PAC-3 cannot provide a reliable and redundant layered defense. The next step is for the Japanese Maritime Self Defense Force to equip its already-built Kongou-class guided missile destroyers, essentially a U.S. Arleigh Burke, with the U.S. RIM-156 Standard SM-3 interceptor and the appropriate software for the already standard SPY-1D radar and Aegis system. The sixth and final ship of the Kongou class, the Ashigara, was launched Aug. 30 and will spend the next year being made BMD-capable and conducting sea trials. The Ticonderoga-class USS Shiloh, a BMD-capable and Aegis-equipped guided missile cruiser armed with the SM-3, arrived Aug. 29 in Yokosuka, where it will be stationed, inaugurating what looks to be a more or less permanent BMD-capable presence for the foreseeable future. 
The SM-3 really is the near-term solution for Japan. It has been successful in six out of seven intercept tests and offers a great deal of flexibility. It can engage short-, medium-, intermediate- and intercontinental ballistic missiles both during the ascent and descent phases of midcourse flight. At shorter range, the SM-3 can reduce the burn of the third stage to a quick pulse to intercept lower-flying short-range ballistic missiles. The kinetic warhead itself contains no explosive but instead makes physical contact with the target, using its phenomenal (and highly classified) speed for destructive energy. 
(click to enlarge) Ultimately, while the U.S. BMD system is looking at a 20-minute-plus flight time for an incoming ballistic missile and finds the long midcourse phase ideal for intercept, Japan has to deal with a flight time of less than 10 minutes (from North Korea, say) and a short midcourse phase. Thus, while the United States will ultimately deploy expeditionary boost-phase assets like an airborne laser and Kinetic Energy Interceptor — still in development — to cover hot spots around the globe, Japan will use these boost-phase assets as part of its regional defense system, along with a terminal-phase interceptor that conducted a successful intercept at White Sands in July. The U.S. and Japanese missile shields will be founded on the same systems and technology. However, they will begin to diverge because of the nature of each state's need for a shield. Japan will begin to make its own improvements to U.S. technology as soon as the United States shares it, with Japanese research and development focusing particularly on tracking radar and software enhancements. In the end, while the United States and Japan have parallel interests in the region — nicely expressed in their cooperation over missile defense — the strategic balance has changed. During the Cold War, Japan was absolutely essential for the United States as a base for naval assets with which to contain the Soviet Pacific fleet. Because of Japan and NATO, the Soviet Union was largely contained to the Eurasian landmass and unable to challenge the U.S. mainland. Although Japan remains geographically and strategically important to the United States, it will be a long while before the Chinese navy is able to threaten the United States as the Soviet navy did. The United States can no longer use Japan as it did during the Cold War. The two nations now stand on much more equal footing politically and economically. While Japan can rely on the United States for help in defending its home islands, it has already come to realize that it cannot rely on the United States to protect its interests abroad. Meanwhile, the United States is realizing that one day Japan could be the regional hegemon with which it must compete for influence — and that each time it helps Japan with new weapons technology, Japan becomes less dependent on the Western superpower. A mutual dedication to a capable missile defense system in the region is a strong new alignment of U.S.-Japanese interests. The next few years should see remarkable levels of cooperation if the political will sustains itself. However, with the end of the Cold War and the rise of Japan as an economic power, both sides realize that their respective political and economic interests will inevitably conflict.
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