摘 要 本文探討美國對1958 年台海危機決策的背景，聚焦在重新思考學界 對華府決策困境短短數年內重現原因的解釋。之前的研究認為：困境重 現是由於蔣介石在兩次台海危機之間大量增防金門、馬祖，想藉此將美 國捲入與中共的衝突，以完成反攻大陸的夢想；美國不願因喪失外島、 大量部隊折損導致台灣不保，甚至東南亞赤化的骨牌效應，故被迫冒擴 大衝突的風險，計劃以核武保衛外島。但本文研究顯示：華府在第一次 危機後未徹底解決外島問題，是因為決策者認為沒必要，況且他們既沒 時間、也沒能力在非危機時期思考外島問題的解決方案；蔣介石在此期 間也未刻意大量增防外島。美國軍方之所以會有以核武防禦外島的計 畫，是因為大舉報復的戰略原則以及減縮軍事預算的雙重限制所致。危 機爆發後，美方竭力避免使用核武，還因此對實際執行外島防衛的地區 指揮官造成相當困擾。因此，從美國整體冷戰政策的觀點來看，或許困 境重現之因較合理的解釋，是華府堅持其戰略原則與自由世界的領導地 位，卻無足夠的資源因應全球防衛需求，才會導致對外島問題既放不下， 也拿不起的窘境。

Abstract This paper has one central concern: why did the U.S. policy dilemma regarding the Chinese offshore islands recur only three years after the first Taiwan Straits crisis of 1954-1955? Consensus has it that in attempting to involve the U.S. in a war with Communist China to realize his dream of returning to the mainland, Chiang Kai-shek deliberately increased the garrison of the offshore islands after the first crisis. Thus, the U.S. was forced to commit itself to use nuclear weapons for the defense of these islands to prevent the domino effects from their loss. But official documents reveal that U.S. policymakers did not solve the offshore islands problem after the 1955 crisis because they did not consider it necessary after having successfully deterred China’s attack. They were also constantly preoccupied with crises all over the world, and preferred the status quo to forcing China to accept a final resolution. The U.S. thus assumed a default position of massive retaliation, making plans for using nuclear weapons to offset an all out Communist attack on the offshore islands. But after the shelling began, Washington tried desperately to avoid implementing these plans. The heart of the U.S. policy dilemma, then, was unwilling to yield any territory to the Communists while lacking sufficient resources to carry this policy out. In a word, the policy dilemma was general, rather than particular to the offshore islands issue.