The T-1A Jayhawk is a medium-range, twin-engine jet trainer used in the advanced phase of Air Force Joint Specialized Undergraduate Pilot Training for students selected to fly strategic/tactical airlift or tanker aircraft. It is used also for training Air Force Combat Systems Officers in high and low level flight procedures during the advanced phase of training. It also augmented or served in lieu of the T-39 Sabreliner in the Intermediate phase of US Navy/Marine Corps Student Naval Flight Officer training until the joint Air Force-Navy/Marine Corps training pipeline split in 2010 and now remains solely in operation with the U.S. Air Force, leaving the Navy with the Sabreliner pending its eventual replacement. The T-1 Jayhawk shares the same letter and number as the long retired T-1 SeaStar under the 1962 United States Tri-Service aircraft designation system.