The ST Aerospace A-4SU Super Skyhawk is a major upgrade project of the Douglas A-4S Skyhawk attack aircraft undertaken by Singapore Aircraft Industries (SAI, now ST Aerospace) in the 1980s and was used exclusively by the Republic of Singapore Air Force (RSAF), serving in the fighter-bomber role from 1989 until retirement from front line service in 2005. Since mid-1999, the A-4SU took on the additional role of being the designated Advanced jet trainer (AJT) aircraft for the RSAF's AJT training program/detachment in Cazaux, France.