A series of small, twin engine corporate jet aircraft, the 400 series is known by several names. The Beechcraft Beechjet 400 with the varying models including the Beechjet 400 and the Beechjet 400A. The next model was the Beechcraft Beechjet 400A also known as the Model 400A, Raytheon Beechjet 400A, Raytheon Hawker 400XP, Raytheon Hawker 400, and then the Hawker Beechcraft Hawker 400XP. The Model 400T is the military version of the 400A. The US Air Force renamed it the T-1 Jayhawk. Over 593 of the civil series were built and 193 military models were manufactured.
Improvements during the series include more fuel efficient engines, an all glass flight deck, and a more aerodynamic shape.