Dap Chhuon affair

1959 Cambodian coup attempt
Part of the Bangkok Plot in the Vietnam War
Date 21–22 January 1959 Location Siem Reap, Cambodia Result Coup attempt defeated
Belligerents
Kingdom of Cambodia	Cambodian opposition Khmer Serei Supported by: United States South Vietnam
Commanders and leaders
Norodom Sihanouk Lon Nol	Dap Chhuon † Son Ngoc Thanh Sam Sary Dwight D. Eisenhower Victor Matsui (POW) Ngô Đình Nhu Ngô Trọng Hiếu Trần Kim Tuyến
Strength
Khmer National Army Khmer Airbone Brigade	Siem Reap KNA regional forces
Casualties and losses
Unknown	1 killed 1 captured

The Dap Chhuon affair, also known as the 1959 Cambodian coup attempt, was the anti-Sihanouk plot by Dap Chhuon, Sam Sary, and Son Ngoc Thanh as well as the supporting roles played by Thailand, South Vietnam, and the United States in the plot. More than any other incident in US–Cambodian relations, the failed Dap Chhuon coup convinced Sihanouk that the United States was implacably hostile to Cambodian neutrality and to him personally. The conspicuous absence of an American warning, however, raised the disturbing possibility that the United States was behind the conspiracy. Dap Chhuon’s coup collapsed without a shot being fired, and CIA operative Victor Matsui’s contact with the rebels was particularly damaging to US relations with Sihanouk.