A U.S. Airman with the 158th Fighter Wing, Vermont Air National Guard participates in dissimilar aircraft training exercise Sentry Aloha Feb. 6, 2012, at Joint Base Pearl Harbor-Hickam in Hawaii. Sentry Aloha exercises are designed to enable Air National Guard units to operate against different, or "dissimilar," aircraft, as fighter pilots will rarely, if ever, oppose aircraft similar to their own in combat.