The flow over a slender body at low angles of attack generates concentrated vortical structures in the wake, which inevitably interfere with the hydrodynamics of a trailing body. This work elucidates the evolution of vortices shed from the leading body moving at low angles of attack ($<6.3^{\circ }$) and their influence on the trailing body through numerical and experimental approaches. Periodically shed vortex rings merge into vortex tubes, forming ladder-shaped packets of hairpin vortices, with the vortex tubes and vortex rings serving as the legs and head, respectively. These interconnected hairpin vortices undergo a topological disintegration process, characterized by the migration of the interconnections between adjacent hairpin vortices along the vortex legs towards the head. The wake vortices interfere with the nearby but nonimmersed trailing body by reducing the pressure asymmetry between its windward and leeward sides, rather than by locally lowering the surface pressure on the side adjacent to the vortices. The dependence of the interference on two nondimensional parameters representing the temporal vortex intensity and the launch spacing is quantitatively clarified. Finally, a theoretical model is developed to predict the hydrodynamic forces and moments acting on the two bodies, including the cross force, axial force, and additional contributions induced by body acceleration and by the shed vortices, with the axial distributions of these forces also characterized.

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• Vortex breakdown
• Vortex dynamics
• Vortex shedding