This paper examines the signature characteristics in spotlight synthetic aperture radar (SAR) image data for surface targets that are executing braking maneuvers during the SAR collection. This analysis considers the special case in which the radar sensor is assumed to move with constant speed and heading on a level flight path with broadside imaging geometry. The analysis concentrates on the target migration effects in which the moving target smear exhibits some defocus in the range direction, although much smaller in magnitude than the smearing in the radar crossrange direction. This paper focuses on the case of a target that executes a rapid speed transition by decreasing its speed within the synthetic aperture. The SAR simulations are shown to give signatures that are in agreement with the predicted shapes.