An assault on the palace–or on the emperor himself–would be an unspeakable humiliation for the Japanese government. In hopes of preventing any attack, the police have launched one of the largest security operations in memory. They have searched buildings and rooftops, probed the sewer system and palace moat, warned the public to keep cars locked, raided eight hideouts and arrested 124 suspected extremists. Nevertheless, the radicals have risen to the challenge. Early this year missiles with an estimated three-mile range narrowly missed the old imperial palace in Kyoto and hit the roof of the emperor’s brother’s Tokyo residence. Since then they have mounted dozens of separate arson and firebomb attacks, including 10 against Shinto shrines.

Japanese officials estimate that 20 extreme left-wing political groups, with as many as 35,000 members among them, are active. Most trace their origins to the ’60s and ’70s, when students protesting the renewal of the security treaty with the United States and other issues donned masks and helmets and battled riot police with steel pipes and Molotov cocktails. Hard-core activists continued the struggle with a violent campaign against the construction and subsequent expansion of Tokyo’s Narita airport. When Emperor Hirohito died last year at the age of 87 and was succeeded by his son, Akihito, they found a new cause.

Radicals charge that the imperial system foments ethnic and class discrimination and encourages a revival of Japanese militarism. Chukakuha, the largest (about 5,000 members) and most active of the groups, rejects the current view of many Japanese that the emperor has become a nonpolitical “decoration.” The organization, whose name means “Middle Core Faction,” argues that the coming collapse of both communism and capitalism will force Japan to tighten its economic lock on neighboring countries. It believes the enthronement ceremony and the Daijosai–a mysterious Shinto ritual held 10 days later–only feed such capitalistic and imperialistic ambitions. The radicals would like to do away with the monarchy altogether.

At least 32,000 police officers will spend the next two weeks trying to thwart their plans; their budget is $32 million. “We’ll see who laughs last,” said Chukakuha spokesman Yoshihisa Fujiwara, 53. The police aren’t laughing. They are determined the emperor’s enthronement will not be marred.