From Japan's perspective, they have no choice. North Korea fired a missile over Japan in 1998. North Korea has also kidnapped Japanese citizens, and despite diplomatic protests, attempted to test both ballistic missiles and nuclear weapons in 2006. North Korea is not the only neighbor of Japan who has done some pretty irrational things. In the past decade, two Chinese generals have made very thinly-veiled nuclear threats towards the United States. From Japan's perspective, East Asia is obviously a neighborhood that is becoming a lot less safe than it was in 1990.
At present, Japan spends about one percent of its GDP on the defense budget (about $43 billion in 2005). Compare this to China, which spends about 4.3 percent of its GDP on defense (to the tune of $81.48 billion in 2005). Japan's relative lack of defense spending still has not prevented it from turning out what is arguably the best navy and air force in the region, one that outclasses even China.
As one example, Japan has 40 destroyers in its Maritime Self-Defense Force. China has 25, only nine of which are really modern. China has 45 frigates, of which perhaps 15 are modern. Japan has nine. Most of China's submarines are very old Romeo-class submarines or the Ming-class ( which is a variant of the Romeo). Only 22 of China's subs are relatively modern. Japan has 16 modern diesel-electric submarines.
The respective air forces also show a technological disparity. The bulk of the 1,250 fighters in Chinese service are J-6 and J-7 models, copies of the 1950s era MiG-19 and MiG-21, respectively. China's only modern fighters are the 200 J-11 (Su-27) and 180 Su-30MKK Flankers. The Japanese air defense force centers around 180 F-15J fighters and 130 F-2s (best described as an F-16 that took steroids).
Japan has been able to keep pace with China with a defense budget that is one percent of its GDP. Were Japan to spend the 2.4 percent of GDP, the same percentage that the United Kingdom spends, its defense budget would be $101.4 billion. If Japan were to spend 4.3 percent of its GDP (what China spends), its defense budget would reach $181.03 billion. What does a Japanese military with those budgets look like? For one thing, Japan easily could increase its military and equip it with modern ships (like the Atago and Takanami classes of destroyers), submarines (like the Oyashio class), and aircraft (like the F-2). Japan also could easily operate several "Harrier carriers" as well, giving Japan the ability to project power. Japan could also decide to build nukes – and has the ability to do so very quickly (within six months).
Japan would have no trouble spending big bucks on arms. The government already spends that kind of money on wasteful, "make work", projects. It's good politics to keep people employed, and it doesn't matter if they are building warships, or highways to nowhere.
Such a buildup would make South Korea, China, and other countries in Asia very nervous. For that reason, Kim Jong-Il's recent nuclear tests are going to make him a very unpopular person in East Asia, where old memories of Japan's conduct from 1931-1945 are still fresh. They would much rather that the potential of Japan's military remain potential, and not become realized. China, in particular, doesn't want to see Japan start a buildup, because they will not be able to keep up. – Harold C. Hutchison (email@example.com)
The North Korean nuclear tests will have the effect of spurring the growth of a new military superpower in East Asia. Japan has, since World War II, not felt the need to re-arm. However, the recent North Korean tests are likely to change that, awakening what is arguably the sleeping military giant of Asia.