Under certain conditions ships can affect the structure of shallow layer clouds. Simultaneous observations of two ship track signatures in stratus clouds from a satellite and in situ from an aircraft show that in the ship tracks the droplet sizes were reduced and total concentrations of both droplets and particles were substantially increased from those in adjacent clouds. In situ measurements of the upwelling radiance within the ship tracks was significantly enhanced at visible wavelengths, whereas radiance at 2.2µm was significantly reduced. Cloud reflectivity along the tracks was enhanced at 0.63 and 3.7µm. These observations support the contention that ship track signatures in clouds are produced primarily by particles emitted from ships.