Last week, Russia delivered 15 additional batteries of S-300 surface-to-air missiles to China, making good on an about 2 billion dollar deal signed in the mid-2000s. Yet despite the publicity surrounding the sale, the Russian-Chinese arms transfer relationship is in trouble. Recent years have seen a precipitous fall in Chinese purchases of Russian military equipment and technologies. Whereas until a few years ago Beijing was buying large quantities of Moscow’s surplus Soviet-era military products, during the past few years the Chinese have declined to purchase any major weapons systems from Russia. China has already acquired about a dozen S-300 batteries...