SAN CLEMENTE ISLAND, Calif. -- The Japanese soldiers in camouflage face paint and full combat gear were dropped by U.S. helicopters onto this treeless, hilly island, and moved quickly to recapture it from an imaginary invader. To secure their victory, they called on a nearby U.S. warship to pound the "enemy" with gunfire that exploded in deafening thunderclaps.
Perhaps the most notable feature of the February war games, called Iron Fist, was the baldness of their unspoken warning. There is only one country that Japan fears would stage an assault on one of its islands: China.
Iron Fist is one of the latest signs that Japan's anxiety about China's insistent claims over disputed islands as well as North Korea's escalating nuclear threats are pushing Japanese leaders to shift further away from the nation's postwar pacifism.
The new assertiveness has been particularly apparent under the new prime minister, Shinzo Abe, a conservative who has increased military spending for the first time in 11 years. With China's maritime forces staging regular demonstrations of their determination to control disputed islands in the East China Sea and North Korea's new leader issuing daily proclamations against the United States and its allies, Mr. Abe's calls for a bolder, stronger military are getting a warmer welcome in Japan than similar efforts in the past.
"This is a very serious rethink of Japan's security," said Satoshi Morimoto, former defense minister, who was an architect of changes in Japan's defense policy.
Until recently, a simulated battle with Chinese forces would have been unthinkably provocative for Japan, which renounced the right to wage war -- or even to possess a military -- after its march across Asia in World War II resulted in crushing defeat. The purely defensive forces created in 1954 are still constrained from acting in too offensive a manner: Last year, a smaller mock assault by Japanese and U.S. forces on an island near Okinawa was canceled because of local opposition.
That recalculation -- a large step in what analysts see as a creeping over the years toward a more robust Japanese military -- could have broad implications for the power balance in the region, angering China and likely giving the United States a more involved partner in its pivot to Asia to offset China's extended reach.
At the same time, the Japanese public has more fully embraced the once-discredited Self-Defense Forces -- partly because of anxiety over China and North Korea, but also because of the military's prominent humanitarian presence after the 2011 tsunami.
Although Japanese liberals and critics elsewhere in Asia fear that Mr. Abe is using regional tensions as an excuse to ram through a hawkish agenda, opinion polls show he has broad public support for his overall policies.
The San Clemente mock invasion was part of the joint training exercises with the U.S. Marines that are held annually. But this one broke new ground. Not only were the soldiers calling in U.S. naval fire and airstrikes themselves, but leaders of their elite unit for the first time helped plan the war game, taking on a role closer to equals than junior partners. And in a reversal of historical roles, wartime aggressor Japan finds itself on the defensive against a powerful China that feels its moment has arrived.
With small but significant steps, Japan has been moving for several years toward refashioning itself and its 240,000-strong Self-Defense Forces into something closer to a true partner of the U.S. military.