Air Force Falcons
Clemson does not have a long history against any of the service academies. They played Army once in 1937 and lost 21-6. They played Navy once in 1939 and won 15-7. Honestly, scheduling any of the service academies would make sense, especially if they could work it out for Military Appreciation Day.
I would pick Air Force because the Tigers have never faced the Falcons. The United States Air Force Academy was founded in 1954 and started its football program one year later.
While Navy and Army have the longest history with a lot of football success through the first part of the 20th century, Air Force has probably had the most competitive program among the three academies. Since the Commander-in-Chief’s Trophy was inaugurated in 1972, Air Force has won it 21 times, with 16 wins for Navy and 9 for Army.
For several years, Air Force was also the only academy to compete for conference titles as part of the WAC and now the Mountain West (Army briefly joined Conference USA, and Navy joined the AAC in 2015). They have won three conference championships and came within a game of playing for the national championship in 1985.