Surface-active films are found in all parts of the ocean. They are easily detected visually on the ocean surface when the wind speed is less than 5 m/s (10 knot). They are generally of biological origin and consist mainly of fulvic and humic acids, carbohydrates, proteins, and lipids. Their molecules have hydrophilic (partially water soluble) heads and hydrophobic (insoluble carbon chain) tails. Surface-active films that have been concentrated at the edges of the centerline wake generated by the passage of a surface ship strongly influence the propagation of the short gravity and capillary waves which interact with electromagnetic waves at both radar and visible wavelengths. An accurate method for detecting the presence of surface films and measuring the fine-scale surface film pressure and surface elasticity distributions on a water surface was developed at the Naval Research Laboratory (NRL). These measurements, together with model-scale flow visualization experiments, have allowed us to develop a better understanding of the role these ship-generated surface-active film distributions play in the formation of the dark centerline and ''railroad track'' or dark lines which are aligned at some narrow angle to the ship's track in synthetic aperture radar (SAR) images of ship wakes. ¿ American Geophysical Union 1992