Wake vortices are made less detectable or reduced in their effect on nearby vehicles by re-orientation of vorticity about an axis in the direction of vehicle motion to transverse vorticity interacting with the longitudinal vorticity. The re-orientation may be by a flapping foil, and arrangements of a plurality of foils moving toward or from each other may be used. Alternatively, fluid may be injected longitudinally between opposite surfaces each having a port so that selective suction through the ports alternately attaches the fluid to the surfaces to deflect the fluid from the longitudinal direction and generate transverse vortices. Oppositely rotating vortices may be formed by separators extendable from each surface to engage the deflected fluid, and extension of the separators may be varied to control vortex trajectory. The transverse vortices may be intermittent, selected for speed, or made asymmetric for maneuvering.