A new method for estimating the aspect angle of ships at sea from an ISAR is developed. The ISAR AutoTrack (IAT) algorithm uses the information from the adaptive motion compensation velocity to improve the tracker estimation of the ship aspect angle and thus to improve the estimation of the ship length. The IAT is based on classical methods of autofocus for synthetic aperture radar. The mean of this velocity yields the error in the in-range component of the ship velocity; the linear time trend of the velocity determines the cross-range component of the ship velocity. Since the IAT creates its estimates during the ISAR time window it is unaffected by ship maneuvers. The IAT has two methods for implementing the algorithm. The Search Method tests a range of errors in course and speed to find the values that best model the data. The Analytical Method uses explicit formulas for the in-range and cross-range components of the ship velocity vector. Both methods benefit from an intelligent smoothing process that removes system errors, random noise, and ocean waves. The goal of the IAT is to measure ship length to within 10 percent over all azimuth angles and ranges relative to the aircraft and for (unsigned) aspect angles from 5 to 85 degrees. To develop a method that satisfies these requirements the IAT is evaluated for three types of tracking errors-errors in the ship speed, course, and Lat/Lon position. But errors in range are assumed to be corrected by routine algorithms in the ISAR processor. Thus, the position error reduces to error in the initial bearing to the ship. The IAT is validated by the analysis of data from an airborne test radar for 22 ship cases. This analysis showed an improvement in the RMS aspect angle from 26 degrees for the tracker to 8 degrees after the IAT. When the tracker position estimate is replaced with the AIS ship position data the error is reduced to 5 degrees; and the ship length error is nearly the same as if the full AIS results for course, speed and position were used. The data analysis also revealed some interesting insights into the effects of shadowing and multipath scattering on the length estimates. Algorithm testing with simulated data shows that the IAT can readily correct for errors in ship speed and course when the initial bearing is known well. However, at higher aspect angles errors in bearing lead to large aspect and length errors. Thus, for the desired range of operating conditions the IAT may need to be supplemented by hardware or software improvements in the bearing estimate. In addition, at azimuth angles ahead or behind the radar flight direction the IAT has a partial blind spot where the cross-range velocity cannot easily be estimated. To remedy this problem the time derivative of the bearing also needs to be estimated, giving a more direct estimate of the cross-range velocity. Recommendations for further development and testing of the IAT are given in the summary.