To understand the potential hazard and mechanism of wake vortex encounter underwater, we perform a numerical simulation on two successively launched projectiles with 6 degrees of freedom. The evolution of wake vortices and their interaction with projectiles are studied under various launcher transport speed and launch sequences. Two major wake vortex structures are discovered: the vortex ring and the counter-rotating vortex pair. As the projectile angle of attack increases, the dominant vortex inside the wake transforms from vortex rings to hairpin vortices, then counter-rotating vortex pairs. The large scale vortices in the wake are highly directional before breaking up, and the counter-rotating vortex pairs can impose significant influence on projectile attitude upon wake vortex encounter. In contrast, minor influence can be done by vortex rings under the same situation. Projectiles launched with higher platform transport speed tend to be more affected by wake vortices due to the strong counter-rotating vortex pairs generated with a high angle of attack.