It's not clear if Japan will accept China's offer; between their own military and the enormous U.S. presence (soon to be complemented by the USS Essex, USS Blue Ridge, and USS Tortuga, all en route), they might not need it. But there's no telling what could happen in the next 24 hours. Disasters and their aftermath are unpredictable; already, 6,000 residents of Fukushima have been evacuated for fear that a nearby nuclear plant could leak radiation.

If Japanese civilians need to be evacuated quickly, or if many more emergency workers need to be deployed, Japan's unique geography means that the best way to move large numbers of people quickly would be with amphibious military ships. But the U.S. Navy's amphibious capability is, at the moment, not at its most capable. Budget cuts targeting amphibious programs, a decade-long emphasis on aircraft carriers and other naval tools that can be applied in Iraq and Afghanistan, and years of delays in upgrading our decrepit amphibious fleet have all left our ability to transport quickly on and off beaches at a low point. But China has a growing fleet of amphibious ships that are new, nearby, and ready to deploy at a moment's notice. Even if it's not by way of amphibious landing, China's massive navy and its proximity mean that, if Japan gets desperate, political and cultural antagonism toward China will probably not be enough to stop them from taking China up on its offer to help.

If China can aid in Japan's humanitarian response to the earthquake, then of course anything that saves lives and helps rebuild is a good thing that neither Japanese nor U.S. politicians will want to stand in the way of, and rightly. But it's important to understand the small but important shift that this would bring to East Asia's delicate balance of power. Over the past year, China has tried many times to project greater influence in its surrounding seas by way of simple, brute force. This has usually backfired, only driving Japan and other Asian states to more tightly unify with the U.S. and against China. Now, China might find that aiding Japan in its time of need could finally bring it the influence it needs. Whether the Chinese navy projects greater influence in the East China Sea and Sea of Japan because it bullied its way in or because a desperate Japan invited them in is ultimately immaterial if the end result is that Chinese ships can sail more freely and in greater numbers.

China's very vocal offer to help Japan could also bring an opportunity for rapprochement between the two nations. Certainly a few humanitarian missions will not overturn centuries of antagonism, nor are they likely to bring revolutionary changes to Japanese foreign policy. But it's precisely these sorts of small diplomatic moments that can open the way to more small diplomatic moments and can, over the course of several years and if things go very well and both sides are willing, give two nations an opportunity for detente. After the December 2004 tsunami devastated much of Indonesia, the U.S. navy brought substantial and much-needed assistance. Though the U.S.-Indonesia relationship was not especially warm before the tsunami, the joint relief effort allowed the two counties to slowly improve ties such that, in only a few years, Indonesia has become one of our closest Muslim-majority allies in the world.