Thailand's role in the Cold War is often seen through the prism of its support for U.S. operations during the Vietnam War. Yet after the departure of U.S. troops from Thai territory in 1976, the Thai government was largely left to fend for itself. Soon after the U.S. withdrawal, a serious crisis arose for Thailand: Vietnam's invasion and occupation of Cambodia from 1979 to 1989. Scholars have examined Thailand's diplomacy during this period but have devoted scant attention to Thailand's defense planning. This article considers both the strategic and the operational dimensions of that planning. The analysis shows that Thailand's strategic culture can explain its adroit strategic-level decision-making and its ability to use its relationships with China, the United States, and the Association of South East Asian Nations to make the costs of Vietnam's occupation unsustainably high. In contrast, Thai military organizational culture can help explain why, at the operational level, Thailand's defense planning was compromised by unclear and incoherent military doctrine, materiel procurement, preparedness planning, and resource allocation.