Modern anti-ship missiles should penetrate the threat of mighty anti-air defense systems. Especially an exposure to searching and tracking radar of CIWS dramatically drops the survivability of the anti-ship missiles. Hence strategies on simultaneous attack of multiple missiles against a single target have been devised. For implementing the simultaneous attack strategy, it is essential to develop the guidance laws to control an impact-time arbitrarily. The designated time-on-target attack strategy is firstly studied where the required impact time is predetermined at homing starting time and then each missile is guided to the target independently to achieve the designated impact-time requirement. We propose the impact-time-control guidance law called ITCG based on optimal control theory, which has a form of the combination of the well-known PN and the feedback of the impact time error multiplied by the time-varying gain. Secondly the undesignated time-on-target attack strategy is studied in which the simultaneous attack can be achieved no matter what the actual terminal impact-time is by reducing the mutual differences of times-to-go of multiple missiles during the homing. For this aim each missile should home on the target cooperatively communicating with each other. We propose the new homing guidance law for many-to-one engagement named cooperative proportional navigation(CPN). CPN has a PN structure with a time-varying navigation gain. The law attains the cooperative homing goal by reducing the variance of times-to-go of multiple missiles by exploiting navigation gain as a control parameter.