Motion tracking sliding-mode control theory is utilized to design a homing-missile guidance law, which induces missile-target line-of-sight angular rate to track an arbitrarily given signal, such that observability for the target tracking with bearings-only measurements is enhanced. An adaptive two-step filter is used to estimate missile-target relative range, relative velocity, and target acceleration involved in the guidance law during the whole guidance period. Simulation studies indicate that the presented guidance law provides good performance for the filter, robustness to estimation errors, and good terminal effectiveness.