Improving critical thinking--defined by one expert as "reasonable reflective thinking focused on deciding what to believe or do"--has been a frequent topic in the writing of history educators at least since the early 1970s. Attitudes and interests do support higher-level thinking and, most importantly, knowledge used in carrying it out is crucial to the success of critical thinking instruction. Even if teaching focuses in an admirably systematic way on cognitive skills or operations of critical thinking, the instruction is likely to fall short if the teacher does not ensure a richness of content knowledge and an atmosphere reinforcing the attitudes and dispositions which motivate and support critical thinking. In this article, the authors describe an activity for teaching the Vietnam War as an element for improving critical thinking skills in history class. The activity is one that fits into what has been called the immersion approach to improving higher-level thinking. By describing the activity as a possible element in the immersion approach to critical thinking in a United States history class, the authors place the emphasis on ensuring richness of content knowledge and an atmosphere demonstrating the importance of critical thinking. The authors believe that the immersion approach to critical thinking as illustrated in this activity can reinforce and develop a variety of important dispositions and attitudes associated with critical thinking. By sparking students' interest in a contemporary and controversial debate, they will be more likely to want to understand important issues about the war and other related topics. The activity also provides the students with meaningful experiences in understanding and considering viewpoints other than their own. By comparing, contrasting, and evaluating authors' points of view, the students learn that factual presentations are not the only objectives of authors when writing about a topic, or of a periodical when publishing anarticle on a topic. The immersion approach is a more effective vehicle for developing students' higher-level critical thinking abilities than approaches that stress specific skills or operations without attention to knowledge and attitudes. (Contains 5 tables and 16 notes.)