Coup Atlas Research Database
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74012121961ConspiracyDissident coup

Japan, 1961 — dissident coup conspiracy

Japan (JPN)East Asia, AsiaDecember 12, 1961

Event Summary

On 12 December 1961 Japanese police foiled the Sanmu Incident, the first attempted coup in postwar Japan. The plot was organised by former Imperial Japanese Army officers and right wing ultranationalists, including Major General Tokutaro Sakurai, under the direction of Kawaminami Toyosaku. The conspirators planned to deploy around two hundred men to storm and occupy the National Diet in Tokyo, assassinate Prime Minister Hayato Ikeda and members of his cabinet, and detain Communist Party and labour leaders, then declare a national emergency and install a regime promising no taxes, no unemployment and no war, the three no's from which the incident takes its name.

Acting on prior intelligence, the National Police Agency launched preemptive raids that morning on the plotters' safehouses, arresting the conspirators, some of them serving Self-Defense Forces personnel, and seizing uniforms, rifles, grenades and swords. The plot grew out of ultranationalist anger after the 1960 Anpo crisis; the only comparable later attempt was Yukio Mishima's in 1970.

Researched Details

Researched

Independent research, added record by record. Hover any label for what it means.

Target identified in Coup Atlas research: Prime Minister Ikeda was unharmed; the plot was foiled before mobilisation and the conspirators arrested
RESEARCHED NAME
Key figures
Hayato Ikeda (prime minister, target)
Kawaminami Toyosaku (plot organiser)
Major General Tokutaro Sakurai (former Imperial Army officer among the plotters)

Sources

The Sanmu incident was an attempted coup foiled on 12 December 1961, during which the National Police Agency arrested 13 conspirators; it was the first coup attempt in postwar Japan.
SOURCE REVIEWED Wikipedia: Sanmu incident open source ↗
The plotters aimed to kill Prime Minister Ikeda and his cabinet and take control of the National Diet, hoping to prevent a communist revolution.
SOURCE REVIEWED Wikipedia: Sanmu incident open source ↗
At the time of the arrests the conspirators already possessed uniforms and weapons such as grenades and rifles, and members included former Imperial Army officers such as Major General Tokutaro Sakurai.
SOURCE REVIEWED Wikipedia: Sanmu incident open source ↗
The plan envisioned installing a regime promising no taxes, no unemployment and no war, and grew out of ultranationalist grievances amplified by the 1960 Anpo crisis.
SOURCE REVIEWED Grokipedia: Sanmu incident open source ↗

Editorial Note

Coded date 12 Dec 1961 is an exact match for the day the Sanmu Incident was foiled. Verified and well documented.

Cross-Reference

Only one dataset carries it. One of the three reference datasets we check against carries this event; the others do not list it. That is not a contradiction — the datasets cover different periods and use different thresholds — but it means the record has had less outside corroboration.

Identifiers for finding this same event in the other datasets:

Cline Center id
74012121961

How the match is made is described in crossref-report.md.

Outcome and Target

Coup Atlas research identifies the target as: Prime Minister Ikeda was unharmed; the plot was foiled before mobilisation and the conspirators arrested.

Baseline coding: Plot discovered and disrupted before execution. Recorded leader fate: remained in office; not physically harmed. The baseline file does not name individual targets; researched names are kept in a separate layer.

Baseline Dataset Citation

Cline Center Coup d’État Project Dataset, v2.2.2
Peyton, Buddy, Joseph Bajjalieh, Michael Martin, and Andrea Gerald. 2026. Cline Center Coup d’État Project Dataset. Cline Center for Advanced Social Research. V.2.2.2. February 17. University of Illinois Urbana-Champaign. doi: 10.13012/B2IDB-9651987_V10
⚑ This citation establishes the coded baseline record; use the claim-level sources above for the researched narrative.

Baseline Source-Document Entries

New York Times

“13 Held On Plot of a Tokyo Coup: Rightist Ex-Officers Planned to Kill Ikeda, Police Say,” December 12, 1961

The Ottawa Citizen

“Ronald Grantham’s Summary of World News: Far East,” December 16, 1961

Wikipedia

This is the citation trail carried by the baseline dataset, grouped by outlet and rejoined from the line-wrapped original. Coup Atlas has not independently re-checked every document; read the original before citing a specific claim. URLs the import damaged beyond safe repair are shown as plain text and listed in citations-report.md. How this list is built →

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