This research investigates the influences on the teaching and learning of English in the Royal Thai Air Force Academy (RTAFA). In the study, a Mixed Methods design, incorporating both quantitative and qualitative research design features, was employed within a Case Study approach. Questionnaires and interviews were used as research techniques to examine and identify what constitute the influences on the teaching and learning of English in the RTAFA and the factors that affect the limitation of the English proficiency of the RTAFA graduates. The quantitative methods included a pilot questionnaire for cadets (N = 35), questionnaires for every Year level of cadets in training (N = 517) and questionnaires for the English instructors (N = 9). The Quest software program (Adams & Khoo, 1993) was applied to analyse the questionnaires and group means and standard deviations were used to calculate effect sizes between students of different Year levels. In relation to the student questionnaire, some category items were also examined and analysed separately. In relation to the qualitative analysis, semistructured interviews with a small number of the RTAFA cadets in all five years of training (N = 25), the English instructors (N = 9) and the senior administrators of the RTAFA (N = 4) were conducted to complement and triangulate the data gathered from the questionnaires. The results from the questionnaires and interviews suggest that the English curriculum influenced the teaching and learning of English in the RTAFA, followed by issues in relation to cadets' attitudes and motivations for studying English and cadets' English educational background. Factors that affected the limitation of the English proficiency of the RTAFA graduates were a lack of realization by the cadets of the importance of English, the very structure of the English curriculum and the content of the English syllabus, the perceived low status of English as evidenced by the lack of academic credits given to the subject, the poor facilities of the language laboratories, the perceived lack of current teaching methods and techniques of the instructors, the varying experiences of the cadets' background knowledge of English, the rigid military system and the need for more native speaking English instructors to develop the oral language skills of cadets. Based on the findings of all the data, suggested recommendations for improving the teaching and learning of English in the RTAFA include a revision of the English curriculum, an improvement of the content of English with an emphasis on listening, speaking and conversation skills, an update of the English language laboratories, smaller English classes and a constant professional development for instructors in relation to techniques in English teaching and learning.