The Military Service Act B.E. 2497 (1954) states that all male citizens of Thailand are obliged to serve in the military upon reaching 21 years of age. High school students have the option of enrolling in the three-year Reserve Officers Training Corps (ROTC) during Matthayom 4–6 (i.e., Grade 10–12). ROTC students drill at a local military installation once per week during the school year for a total of 80 hours, with field training exercise at the end of the second year (over the duration 3 days) and third year (over the duration of 5 days). The ROTC program is operated nearly exclusively by the Royal Thai Army, with recent introductions by the Royal Thai Navy and Royal Thai Air Force, but both with more restrictions on entry (e.g. students of schools near a naval or air force base used for training only). Those who complete the three-year program are exempted from conscription and receive the rank of acting sergeant (E-6) upon graduation from high school. Students who do not complete the program or wish to enroll in the commissioned officer phase of the program can do so at their post-secondary institution. Those who do not complete the ROTC program will be required to report for conscription in early-April of the year in which they reach 21 years of age.