The Red Army Faction originated as a schismatic militant sub-faction of a larger New Left student organization called the Communist League (共産主義者同盟, Kyōsanshugisha Dōmei).
"[6] Meanwhile, the group planned more significant attacks against government agencies and the Prime Minister's official residence, for which they began "training" at the Daibosatsu mountain pass northwest of Tokyo.
However, on November 5, 1969, having been tipped off by informants, police raided the inn where the student militants were sleeping, arresting 53 group members (including many key Red Army leaders) and capturing detailed plans for the intended attacks.
In early 1970, Shiomi began making plans to hijack a Japanese airliner, codenamed "Operation Phoenix," that would allow group members to fly to Cuba and continue their training.
[8] However, by this time the loss of Shiomi's ideological leadership, combined with relentless pursuit by police and continued arrests of key members, had taken a severe toll on the organization's cohesion.
Those that wanted to relocate overseas became the Japanese Red Army, led by Shigenobu Fusako and Tsuyoshi Okudaira, while those who wished to continue the revolution at home in Japan joined forces with the Kanagawa prefectural branch of the Revolutionary Left Faction to form the United Red Army, led by Tsuneo Mori and Hiroko Nagata.