The T-37B became operational in 1959. The T-37B has improved radio navigational equipment, UHF radio and redesigned instrument panels. Many air forces fly the T-37B, including those of Thailand, Greece, Chile, Jordan, Turkey and Pakistan. Students from 12 North Atlantic Treaty Organization countries train in T-37B's at Sheppard Air Force Base, Texas. The preflight phase of Specialized Undergraduate Pilot Training [SUPT] takes three weeks and consists of academics and physiology training to prepare students for flight. The second phase, primary training, is conducted in the twin-engine, subsonic T-37, a rugged aircraft equal in maneuverability to most of the fighters of World War II. Students learn aircraft flight characteristics, emergency procedures, takeoff and landing procedures, aerobatics, and formation flying. Students also practice night, instrument and cross-country navigation flying. Primary training takes approximately 23 weeks and includes 254.4 hours of ground training, 27.3 hours in the flight simulator, and 89 flying hours in the T-37.